2001 Saturn L200 engine or transmission

Sounds like you have a few problems going here. For the oil leak, it could be the front or rear crank shaft seal, but you'd have to clean everything off and trace it back to see where it's coming from. If it's coming from the rear of the oil pan, more then likely it's the rear main seal. Question tho. Are you sure it's an oil leak and not a transmission leak? Because if the transmission is low on fluid that may lead to your other problem of not moving in drive.
As far as the flicker lights. If they flicker when you put your foot on the brake, then you could have the incorrect bulb in one of the rear sockets. Also Saturn has a recall on the rear tail light assemblies. See if that's been done, that might fix the flicker.