Right now the latest on the gear is take a pair of side cutters and cut the flat on the crown/pinion gear off this provides room for the two gears to slide past each other the tought is that the flats on the ring and crown go solid and push themselves apart, thus the slip.
The cars were running this at Nats and according to Peter there were no stripped gears talking to Fred today at TA he has done it to his car also and has still stripped one but the occurance is alot less now.
Dave has a plate that was machined to fit against the gear and help clamp it and provide more support it is not a Tamiya part and I don't think there are plans to make it.
I have had a friend machine a spool for the car the provides support in the same place as Daves ring and Pete said he had no issues with it either.
Hope the info helps, try the mod and see if it works
Dan