Check for chips on the crown gears. If you have the remains of the tooth could be imbedded in the pinion gear which will chew up the rest of the crown gear.
If not it sounds like your crown gear and pinion gears need a good dose of molly grease. I do mine once every six weeks, plus it's a good time to top up the diffs and inspect the gears.
Put electricans tape where the centre shaft bearings sit on the upper and lower casings. You'll be amazed at the difference. I love my 410R, I wouldn't change it for the world.
