My brother is dropping off his 1993 164L with manual transmission, 203K miles, for me to do some maintenance. His biggest complaint is an oil leak at the rear of engine, it drips onto the exhaust pipe, leaves a pretty big puddle on the driveway lately. I'm guessing it is the rear main seal. How can I be sure it is the rear main seal? Is there anything easier I can do other than replacing the rear main seal (maybe some type type of oil additive sealant)?