I noticed a few threads talking about changing rear main seals. Here is a video about doing it on Vortec and LS engines. For those used to small block Chevy's this is a bit of an eye opener. The video starts off with the transmission and flex plate already removed. The video has better lighting than that available doing it underneath the vehicle. In real life the exhaust would be dropped and transmission and flex plate would be removed. (for 4WD, the transfer case needs to come out as well. ) The guy uses a $50 centering tool available from Jeggs or Summit. At 10:42 he pushes the new seal into place. Enjoy.