Oil Filter leaks

Bob,

I presume by "the main gasket", you are referring to the rectangular cross-section O-ring that seals the rim of the oil filter canister to the oil filter housing. If so, I am aware of two possible problems:
1. Some vendors supply an O-ring that is too wide for the groove in the oil filter housing. If you have to squeeze it into the groove, it is the wrong part.
2. You may have more than one old O-ring in the groove. When they age, the O-rings become hard and brittle and can be compressed into the base of the groove. So much so, that a previous owner may have put another on top of the old one without realizing it. This was the case on my car, and I have heard of others with the same experience. Take a sharp pick and make sure that the groove is entirely cleaned out. It should be deeper than the width of the new O-ring.
If you have the right O-ring, and a properly cleaned-out groove, you should not have a leak. I have changed mine more times than I can remember, and never had a leak. In fact, this is about the only place on my engines that does not leak oil!
As for fitting a spin on filter, if you have either of the above problems you will end up with a leak between the oil filter housing and the spin-on filter base, so you will gain nothing...

Good luck.
-David