Before you go at it hammer and tong, I would suggest a conservative approach.. It is very unlikely that the lip of the rear main seal has been reveresed or even damaged, so it might not have to be replaced. More likely there is pressure being built up behind it in the crankcase and it is the pressure that is causing the leak, not a failed seal. First go in and replace or gut the flame arrestor, and make positively sure that the crankcase breathing hoses/ducts are clear. Warm the engine up completely and slowly remove the oil filler cap with the engine at idle. Observe for "excessive" puffing or expulsion of crankcase gases. If the crankcase gases are obviously puffing away out of the oil filler opening the piston rings could either be worn out or just gummed up and not sealing against the cylinder walls. Before you tear the engine down to replace them change the oil and filter substituting a large can of Marvel Mystry Oil for the last quart of oil. Drive the car as you normally would for at least 500 miles topping up the oil lost due to leakage as necessary with standard motor oil. After 500 miles (preferably more) change the oil again using only standard motor oil and do the oil cap check test again. If the puffing is eliminated you have saved yourself a zillion bucks for the engine tear down. If the puffing has gone, clean the engine up at your local spray car wash. Pay special attention to cleaning the bell housing top and bottom and the seal areas on the front of the engine. Drive the car for about a week before worrying about the rear main seal leakage again. This will allow plenty of time for any residual oil that has been thrown around in the bell housing to drain out. If after a week there is STILL significant oil leakage from the rear main seal you have my permission to replace the seal. If the puffing is still apparant after the Marvel Mystry Oil routine and second oil change you will have to go into the engine to do rings, bearings, etc. At the same time you will of courase replace all the front seals and the rear main seal. If you just go in an replace the rear main seal without going through this little process the chances are that you will be wasting your time and money. You don't have to do all the dirty work if you don't want too. Just take the schedule as presented to your technician and tell him that you will do the driving if he will do the changing and you both can do the looking.