Sorry for the slow reply - the site (for whatever reason) didn't notify me (as it has historically) that somebody had posted to this thread. I just happened to peruse the site, noticed your writing.
Anywho, congrats again on your decision and successful recovery. You did the research, exhausted the alternatives and (after a diligent hunt) found'a qualified surgical team - you should be very, very proud of what you've accomplished - and I couldn't be more happy for you.
As to lifting; like you, I've given up dedicated leg training beyond stair-climbing and lunges. That means no deadlifting, squatting, extensions, presses - any movements that might place intense stress on areas that now contain or are near tubing, cylinders or the like. Moreover, I've also ended focused ab(dominal) training as well. Crunches or similar that would place dedicated stress on the abdominal wall (and so the vicinity of the reservoir)...for me, also a no-no.
Now, that all said, I gotta say that I made this drastic alteration to my lifting routine (and despite the changes they've especially wrought on my former six-pack) solely on my own. My surgeon gave me no such prohibition - made no warning that training my abs or legs would or could result in damage to the implant. Indeed, my surgeon stated there were no limitations
to life with the implant (beyond perhaps cross-country horseback riding or trying to hump concrete walls while inflated). Rather I came to the decision (to limit my training) alone, and because I figured that, while yes, the implant doesn't limit "regular" daily activities such as walking up stairs, bending over, twisting and turning, etc. - its designers never designed the thing for a 20 - 30-something bodybuilder and the daily activities they would engage in a gym environment. I mean, how old is the "typical" recipent of one of these things? 65? 70? With certain, limited exceptions (I've seen some truly inspirational guys now and then at the gym), there ain't a 60-something year old on earth that's gonna hit the weights with the same frequency, intensity or duration as'a 30 year old bodybuilder...and so, as'a strictly precautionary action, I've chosen to limit how and what I train despite statements by "the experts."
Now, that all said, while I've strictly limited leg training and omitted abs, I still hit other muscle groups with the same intensity as before. Training biceps, back, shoulders, chest, etc...these exercises/muscle groups should have zero impact on the implant, and indeed, I've felt nothing "down there" and seen no change in the daily performance of my device, regardless of how hard I hit it in the weightroom. And for the record, my regular, daily routine is never less than an hour of pretty intense weight training, and often lasts as long as two.
To answer your specific question about sitting on benches/chairs or resting against pads on certain exercises...yes, if seated on'a particularly stiff (poorly padded) bench, sometimes I'll feel a slight pinch or whatever. In such case, as with sitting on any uncomfortable surface, I'll just adjust myself such that I'm comfortable. I'll also seat myself (initially) so that my chest primarily rests against the pad, and not my stomach or manhood - a position that's not only more comfortable, but "safer" (I'd wager) for the implant as you go about pulling, pushing and generally grunting. Shoulder presses should be no big deal...I don't know how the pump moves about inside our balls as we sit, twist, etc., but I'd wager that when we're planted flat on our butts, the thing just moves to the side...and because I've experienced not only zero mechanical issues post-shoulder training/sitting/pressing, but more importantly, zero pain or other discomfort while in this position.
My advice then is to just go about your routine (even training legs if you're so inclined) and simply when and if you feel any discomfort, just stop or adjust what you're doing. The device really does seem to be as durable as the doctors and others here and elsewhere have stated, and if it does break, it's not gonna be because you were (bicep) curling or shoulder pressing too much weight. Good luck - now go get huge!