When the box was out of my cossie when I changed the clutch I had the flywheel refaced. So I wiped all the crap off the back of engine. refitted it all to find I had a oil leak. I'd wiped the sealer from the end of the sump gasket when cleaning so I degreased and wiped some more in job done.

And yes the cvh sump gaskets are a pain to seal.