1971 Buick Skylark rear main seal

This is what is called a rope seal. You'll have to drop the oil pan, which means jacking the motor up to get it out and having the crankshaft at a certain position to get it out. Then you'll need what is commonly called a "chinese bandit tool" your rear main will have to be pulled out as well. You need the tool for the top piece as you can replace the bottom one easily. They wil have to be cut even with the caps and then using a dab of silicone to ensure no leaks. Before you put the cap back on and retorque it.