904 guru

Only thing on my car I havent done personally is the 904 trans.Have had 2 different people do it and both have failed.1st one lasted 50 passes,2nd one about 200 before it cooked the front clutches.This is a slant six car with about 280 rwhp that runs in the mid 11s all motor.I need better guideness,any hints or tips welcomed.Guzzi Mark