I have an older contractors saw that is presently in "retirement" but I remember it going out of alignment and when I checked underneath I had found that the mounting bolts had worked themselves loose. Check to ensure that the table is mounted securely to the base and the same for the trunion to the table. When I finally figured it out some of the bolts had backed out considerably.
Also, I used to find that munge would build up at the positive stops and I would have to get in there and constantly clean them up so I could get it back to 90 degrees or to the full 45 degrees. Different problem I know but one I constantly battled with the saw mainly because I was using it to trim houses and it was all pine so resin build up was a nightmare.
He who laughs last, thinks slowest