No, the nylon idlers will not last under even mild BL. Upgrade to either the UE idlers or the set RC Monster sells (hardened, lightened steel). Then there is a flimsy, thin roll pin on the input shaft (top shaft) that secures the gear at the end. This is a fairly easy fix - remove old pin and fashion replacement from a allen L wrench or the shank of a drill bif of the right size. The allen wrench was easiest - takes a little filing on the points to get it to fit and still be tight.

Eventually the gears will go, not sure which, but they are not made to handle BL power. You can minimize probs by locking it in 2nd (just leave it) or doing gorillamaxx 1 speed conversion which just leaves 2nd gear in trans and discards the rest.

My 3906 is locked in 2nd and has the UE idlers and has been OK with an 8XL that I have esc turned all the way down for. Low power setting was enough I still killed the diffs and twisted the stock axles. I upgraded to 3.3 knuckles, bulks, turnbuckles and wheel drive axles. I used UE TI center drives. I replaced the diffs with stock 16.8 diffs. Been solid since getting all that done.