This is very helpful. There is a factory mark on the pot where it was
originally adjusted, and I moved it about .5mm counterclockwise; I
could reset and measure. Regarding the rails, it does not seem as
though there is any potential for adjustment; they just "clip" into
place.

When you say to adjust the pot using a standard CDROM, I am assuming
you mean a music CD (as this is an audio CD player), or is there some
trick to using a data CD?