4 years in........need advice.

Well you can learn things, and then forget you've learned them. Habits, assumptions, wants, expectations. I think one of the traps is thinking you've gained the ability to make things happen, and that all of your past successes were because you learned how to achieve it. So it would follow, that exerting complete control over your session should (at least sometimes) yield the results you've had before.

But I think what you should consider is that there's something unseen, something else happening in those sessions that you weren't aware of, or in control of. Something you might not even have noticed.
I think as our sense of competence, and confidence grows, we can get tunnel-vision... the scope of what we consider valid controls/inputs narrows to the exclusion of things we're not aware of.
But it's the beginners mindset that we need to open that back up.

Frustration is hard to deal with... not getting what you need creates a problem to be solved. And when we go about trying to solve a problem, we look at what tools we have. Maybe the tool you need is one you've never noticed, or have forgotten about. And maybe the next step for you is to stop trying to use the tools you know about, and let your body discover some new ones.

An exercise/fantasy I find helpful is to imagine you've been somehow transported into the body of a woman... it's easy in this case to accept that things work differently, and that you're somewhat passively accepting the aneros' movements inside of you. I find it easier to detach from my expectations that way... I'm not craving for an ejaculation or any specific kind of feeling.

I'd challenge you to shed the idea that those past good experiences were the result of an ability you had. Because it assumes you can control and manipulate all the inputs. Sometimes you have to throw away all your experience and have a session where "anything goes". You give up thinking you know how anything is supposed to unfold, you stop pre-empting every sensation with the question of what feeling comes next, or how you can shape what you're feeling into something else.

I've found erotic hypnosis mp3s pretty useful for practising a "just let it happen" mindset, but that's a whole other learning experience.

It sounds just like a dry spell, which for some of us can last a week or so, but for you it's lasted 3 years!! During a dry spell I have to say your description of trying to get an orgasm sounds just like how it goes for me, and I find myself thinking what is going on?? I could do this last week no problem and now absolutely nothing I just can't orgasm. It feels good but it just won't turn into that magical orgasm.What I often find is that I'm then trying too hard and the disappointment creeps in fast and I'm thinking "is that the start of an orgasm? No, maybe that is, No, is that? No" and then I get tense and just know it's never going to happen. I get into the negative mindset of not expecting it to happen, or is it that I AM expecting it to happen and my expectations are too high.

What I found broke my last dry spell was cultivating a very passive mindset of saying what the hell I will just enjoy it anyway, so what if I ejaculate, or orgasm, or not, and placed myself as more of an observer just watching to see what sensations I would get, not hanging onto them or registering any emotion related to them. I also used a very passive sexual fantasy and visualised it in great detail. It worked wonders, and I have used that mindset over and over to good effect.

Basically you aren't in control, and I agree with @Clenchy's advice. You are only creating good conditions for an orgasm to come along, it will find you, and when it does you hang onto it and enjoy it.

In Buddhism there is something called the five hindrances to meditation, and I always think they are very relevant to aneros: 1) Sensory desire 2) Ill will 3) Sloth-topor 4) Restlessness-worry 5) Doubt, and those can all be applied to MMOs. If any of those are present then an aneros session will not be good. Another interesting link between aneros and meditation - worth looking up and reading about if you are so inclined.
Also interestingly the five factors that counteract the hindrances are: 1) Examination 2) Investigation 3) Well being 4) Bliss 5) Single pointed attention.

I would say I have advanced a noticeable amount in the 3 years I have been using aneros, but I have somewhat similar experience. I would say the best sensation I ever felt with Aneros, and the only time I was really taken over by pleasure as opposed to bumping against it trying to gain entry, it was in my first few months. In the 2+ years since then, my sessions have gotten gradually better and better but never reached that peak that took me by surprise.

@mkts I'm really interested to hear you say that.

My experience is very much the same. In the first WEEK of using the aneros I had something very special happen. I have never managed to go to that place again. I have had some great orgasms, but in terms of being taken for a ride (and I was taken somewhere very special) it has never really happened again in quite that same way.

It affected me so much that I took a great interest in meditation. I have read a lot and the same is described when people experience the higher jhanas by accident when they first start meditating. It generates a great deal of yearning for it to happen again, it's almost painful, and yet it won't happen again, not until you are ready for it and until you truly stop yearning for it and desiring it.

I went into a session last night, and noticed I've been doing something really wrong for a long time. When pleasure starts, I have a habit of retreating from my body and going to this small room in my head... like a squirrel grabbing a nut and running away somewhere safe to gnaw on it.
It's very weird, like some kind of dissociation or some manifestation of 'Terror at the gates'. What I'm doing at the same time is applying a limiter to the pleasure. I could actually feel myself doing it, and had to tell myself to stop. @smudgefish - I think this is where my eye-tension comes from as well. Some part of me is recoiling and retreating from it... almost as if someone is about to punch me, I can see the "wind up" coming, and I'm curling into a ball. I've never seen it so clearly as last night. And it wouldn't surprise me if this was bringing up some old shit from my past.

I should add that this was my best session ever, and 100% a rare super-o. Like someone pouring warm buckets of water down my back, frying my circuits. I think that I managed to "stay in my body" for it, and take my foot of the brakes.

Anyway, this is relevant to my previous post because I've been unknowingly doing this for years. It was something I just did, and never really noticed, or thought anything of. It's really giving me a lot to think about.