When your crankshaft gets turned down to get rid of any grooves in it, do you need to get an undersized rear main seal or does the regular sized one work? do they even make an undersized one?
It is a thin sleeve that slides (presses) on over the crank to provide a new smooth surface. Then you use the accompanying seal that comes with it, since your crank diameter is now different than stock.
I still say having your machine shop dictate what to do is best (sleeves are normally used when doing a RMS with the motor in the car, and seeing that the crank is all grooved up and will allow the RMS to leak again).
oh.... the problem at hand isnt that my crank is grooved up... it is that the crank was already turned down, reinstalled and a regular sized seal was put back in... now i have an oil leak