I have a $2 flea market older half-sheet Black and Decker pad sander
that runs great (9000 rpm), but its side to side movement is
uncontrollable. It makes no difference how hard I press on it. I
flattened the platen on my belt sander and that didn't help. I took
off the bottom, and the rubber posts look fine, and nothing seemed
amiss there. What to do?