OK transmission gurus, here's one for you.

The car is a 2003 Hyundai Accent, about 98,000 miles.

1.6L DOHC motor, 5 speed manual transmission.

The synchros are getting weak on 2nd gear, and it will crunch going in (up or down) sometimes, but here's the strangest part:

It doesn't do it with the A/C on.

Now, my thinking is this: Since the problem gets worse after pulling a long hill or sitting in traffic, I'm thinking it's happening once the transmission reaches a certain temperature, and on this car the A/C immediately kicks both cooling fans on regardless of temperature, so could it be cooling things down underhood just enough to thicken the oil up a little? It's running Redline synthetic right now, plus some friction modifier, and it's a little overfull (maybe half a quart or so).



So here are my questions:

I've been reading that synchros require a little bit of friction to work properly, which makes sense with the heat making the problem worse, and the friction modifier helping some (but not curing it). Do you think switching back to regular gear oil would help?

And, if so, would going to a thicker gear oil help? Transmissions can be had fairly cheaply for this car, but at the same time I don't want something that's just going to do this again in X number of miles.