5th gear synchro is just about dead.
 

Im switching to Redlin MT90 this weekend, buying the oil today. Right now I have Redline ATF/Manual fluid in there which worked great in the cold, now its too warm.

Third gear grinds when cold.

I guess 145k miles is pretty good. Still drivin it.

seems like all rx-7s grind a bit in 2nd when cold - even if you let the engine warm up.

Engine warming up doesn't help, because you have to get the tranny hot, which you do by driving it :)

Speaking of such things, my tranny is all goofed up too. 5th syncro is GONE, I aboslutely must double clutch on the 4-5 change or it goes grindy grindy. The 1-2 and 2-3 shift don't grind, but if you're on it hard they won't go in, it feels like there is a piece of rubber it's pushing up against (springy) I think my shifter bushings need replacement, tho it might be the whole trans (shudder)

I actually hear its a pretty common problem, grinding 5th gear. I think Im going to save my $35 bux on the redline and double clutch it. I dought that oil will help it any.

Besides. You never get past 2nd when autocrossing.

I have never grinded in any gear. Guess I am just lucky!!;)