A photo would be very useful, yes. As described the issue could be an "Analog" problem, or it could be something messed up with video memory addressing, and the angles of attack for those things are very different.
The quick "try this" is there are two small variable resistors which can be turned with a small screwdriver on the side of the logic board in front of the power/cassette/video ports. (Only accessible with the case taken off, of course.) They affect horizontal and vertical pulse timing. I forget which is which but fiddling with them should make it obvious. It's possible adjusting the vsync pulse timing will fix the positioning issue, but it's not "usual" for it to drift drastically.