HELP! ( totally OT) - Hitachi Monitor problem

Hopefully someone will know about this . . . I've got this really "comfortable" 20" monitor (Hitachi CM2085) which developed a rapidly fluctuating left and right margin, which apparently is related to its pincushion controls in some way. Not being in any sense expert in repairing monitors, I fooled around with the various accessible controls, (after removing the plastic outer shell) such as "side-pin" among others, and managed to get the horizontal line length to remain relatively stabile, though the screen now has a huge pincushion distortion, which I can make go away somewhat, but when it's gone, the rapid left/right margin fluctuation comes back, though somewhat differently than before. Is anyone familiar enough with this monitor or with monitors of this type to make any kind of suggestion which might help alleviate this problem? thanx Dick