Shoulder trouble and overhead presses: What to do?

[lyorn]

Due to a combination of too much time at the computer, a suspectability for arthrosis, and an accident caused by attempting to out-stubborn a yoga exercise, my right shoulder is a mess. Mobility is limited (slightly: I can still get my fingers together behind my back with left arm top, right arm down, but it hurts), stability isn't what I could be, and it hurts most of the time. The doctor I visited a good two years ago sent me to manual therapy, which helped, but getting back into the gym helped more.

However, now I'm doing heavy lifts, inlcuding overhead presses (dumbbell and barbell variant), and front squats. And I feel that my shoulder actively hates them. The trainer in the gym confirmed that these moves strain the shoulder tendon, which seems to be involved in my problems anyway. However, there is no trainer in the gym (anymore) with a specific heavy lifting background (or I just do not want to accept "no more heavy overhead lifts"), so I'm asking here:

I wish to continue the heavy lifts, including overhead, but I do not want to mess up my shoulder completely. What to do? Maybe supportive/flexibility exercises?

ETA: To all, sorry for taking so long to reply. I try to limit my computer time, because, shoulder. :-S