Many threads on this forum on that topic - use the search feature. You will see that question has unleashed an avalanche of replies. If you are looking for a consensus answer, your chances are slim - many opinions! :confused:
fyi, the manual on recent models calls for engine oil (e.g. 10W40, etc.) - don't now about the '96...
KDX 80? Didn't know they had one. Anyway, on transmission oil, I use Bel-Ray or Maxim 80wt and change every 3 rides. Seems to shift best if I change frequently. I also miss 2nd gear now and again, don't know if it's a problem with the bike or if I don't lift up high enough to get back neutral and into 2nd, but this phenomina happens less if I keep the tranny fluid fresh.