I'm currently running M1 filters in my Pentastar. The first one had over 7k on it and came out in excellent shape, but I noticed something interesting. Awhile back, in taking apart a Fram Ultra for this application (cartridge filter), I pointed out that the media was VERY strong and was backed by a grid of what appeared to be a super strong polymer, nylon, or monofilament material. It took vice grips to tear it apart, along with a surprising amount of muscle effort. When I shared this either here or on Jeep forums, someone said the M1 cartridge filter would have metal backing on the pleats. Well, I just took apart that first M1 filter with 7k+ on it and while it was fine, and did its job well, the pleats were not backed by metal, polymer, or anything. They were just the filter material, and they came apart relatively easily.
I've not had an M1 with a known problem, but for my application, it is not in the same league as the Fram Ultra. Not even close.
