Also a fan of the M-1. I tried a Fram Ultra, but I had some seepage around the gasket. It sits inverted on my Tacoma. Maybe I screwed it on too tight, but I've never had problems with the M-1.
I am currently running a Royal Purple though, and plan to use it for 2 5k OCIs.
I usually cut the M-1's open, and there are never any negative surprises.