How do you repair an engine rear main seal leak?

The first thing you should do is check and replace your positive crankcase ventilation (PCV) valve if it's plugged, and make sure your engine oil level is not over full. Both of these conditions can cause your rear seal to leak. Check these and correct them, then see if the leak continues. If not, then you're good to go. If it still leaks, see below.

Answer

Replace rear main seal. Transmission must be removed.

I have replaced the rear main seal on pre-1987 small block chevy's without removing the trans. Not sure if it would work on other engines. Pull the oil pan and the rear cap. You may need to loosen the other main caps to take the pressure off the seal. Use a piece of thin wire to push the upper-half seal far enough to one side to get ahold of it and pull it out. Push the new seal into position, replace the other half in the cap and reassemble.