Matt, once the gears are loud, the chances are they're shot and you need new ones whatever, a new idler and diff gear should be not much more than a fiver, check the layshaft too, though that should be OK. Internal gears are a consumable part on any car, they last a lot longer than other parts but they do wear out, once noisy they are likely too far gone!
I much prefer the Losi shocks, it's funny Losi shocks on a B4 seems to make it worse, yet Losi shocks on an X6 seems to make it much better
I hear on the grapevine Chris' X6 took TQ in round 1 yesterday at Teeside by a few seconds and there was a few in the A again
