Look on the back of the focus track. On the sliding part, there screws with springs attached. At least two (I don't remember very well) of these screws are the adjustment for l/r alignment and they are also the adjustment for wear in the slider. It's a very fiddly process to get the alignment right without leaving the slider too tight or too loose. If the wear plates in the slider are badly worn, it probably won't stay in alignment. I am basing this on my old 45M, which I'm sure uses the same chassis. Also, measure from the baseboard to the bottom cross member to make sure the gears on one side haven't jumped a tooth. It should measure the same on both sides at any given height. My 45M was worn pretty badly and I finally made an adjusting plate with screws to give l/r adjustment on the lens stage. That pretty much eliminated using tilt for perspective correction but I've never used it anyway. It sure makes life a lot easier. These are a good old nearly indestuctible enlarger, but alignment has always been a headache and not many know how to fix it. Good luck---