Owners of some 2010-2012 Chevy Express and GMC Savana vehicles equipped with the 6L90 automatic transmission may comment on a transmission fluid leak at the rear of the transmission. This condition may be mistaken for a leak from the propeller shaft front slip yoke oil seal.
The condition may be caused by a missing propeller shaft slip yoke welch plug. This is the plug that is pressed into the outer end of the slip yoke under the U-joint. A visual inspection of the slip yoke will show if this plug is in place or is missing.
If the welch plug is missing, replace the propeller shaft front slip yoke and the universal joint only. Do not replace the slip yoke oil seal.
If the slip yoke welch plug is in place, use automatic transmission fluid dye to help isolate the source of the leak.
19209351 Yoke, propeller shaft front slip
15898097 U-joint kit