I have sealed 40+ tanks using Red Kote with only one mishap, in that case I did not allow the Red Kote to fully cure and the tank weeped a little staining the paint red.
The key to an effective result is getting the tank very clean to begin with, then allowing the Red Kote to fully cure. I think from a time/material/hassle perspective, cleaning the tank and sealing with Red Kote beats separating a tank to replace a gasket, particularly if the entire crankcase is involved. In the case of the McCulloch AV 10 Series saws, the tanks and screws are sealed with epoxy so getting the tank apart requires a significant effort including drilling and tapping the broken off hardened screws.
On saws like the Homelite SEZ models, sealing the tank with Red Kote is far more cost effective than splitting the crankcase to replace gaskets and reseal everything.
That's my perspective anyway.
Mark