If you have a Northstar powered FWD Cadillac your "rear main seal leak" may actually be coming from your cam cover

My 2002 DHS with 86k showed all the classic symptoms of a slight rear main leak...Occasional slight whiff of burning oil at traffic lights and after pulling inside garage. Oil dripping from rear of engine (driver's side) and landing on the exhaust crossover. Everything else underneath was clean and dry.

The oil was coming from the rear (driver's side) corner of the cam cover closest to the firewall. Hot oil was dripping down the back corner of the engine, appearing in the bellhousing and falling on the hot exhaust. I found that I was missing a cam cover bolt.

Moral of the story is check your cam covers. I was all set to book an appointment for a rear seal replacement but will be picking up a bolt instead. I suppose the worst case scenario would be replacing the cam cover gasket or perhaps removing a broken bolt.