[Sylvester]

The same thing happens on my eight-e running a mmm/neu 1512 2.5D/f (2050kv) on 5s. Try 10k fluid and it should lower the temps a bit, but if your running the stock steel spur it will get warmer then usual since heat from the pinion coming from the motor transfers onto the center diff.

I run the losi smart diff now and it doesnt get as hot, it also eliminated the front tires from ballooning and it has better acceleration.

If the thicker fluid doesnt help try putting some grease into the drive cup where the cup and pins meet, it should reduce some friction that happens. Other then that you shouldnt have to worry to much about getting hot drive shafts.