[Sirrotica]

From someone that has done rear main seal replacements, many, many times your mechanic is mistaken if he thinks he can drop the pan on a Pontiac Stratosteak engine, in chassis, (a feat only for the very determined), pull the rope seal out, and replace it with a 2 piece lip seal, and then not have it leak.

The probability of success would likely be 10%.

If it has a factory crank in it the serrations will soon abrade the new seal. The crank should be pulled to smooth the serrations so they won't abrade the new seal. If you should somehow get the new seal to not leak upon fire up, it will leak soon after, simply because the serrations will cut the lip off of the seal.

Save yourself time and money in the long run, and remove the engine, put it upside down on a stand so you can work on it comfortably. You'll have a much better chance of success if the engine is out of the car.

If you don't want to pull the crank out, and smooth out the serrations for either the 2 piece seal, or the 1 piece seal, you would need to try the graphite impregnated rope seal. Best Gaskets makes them, as well as do other companies.

If your guy tries to do it in chassis, I can tell you he'll probably never do a second one, and the success rate is very low, compared to pulling the engine, and doing the repair on a stand.

My advice is to always pull the engine and in the long run save you time, money, and a great deal of frustration. That advice goes for any rear main seal you choose to use in your engine,

I can't truthfully comment on the 1 piece or 2 piece, as I've never used anything but rope seals, someone else will probably comment on their luck that has actually used them.