The Advance Auto Parts store I was at had the Pure One filter (PL15505) on the shelf - the felt ring on those was worse than the L15505 version. I am guessing that it was a Q.C. problem or maybe the ones that fail Q.C. for Motorcraft end up with the Purolator name on them. I only bought the ones with the felt ring that looked the same as the OEM.

The L15505 looks just like the OEM filter while the PureOne filter is yellow in color (IIRC).

Still haven't dissected the filters yet - once the ankle is better maybe...

Should probably do some tests on the o-rings as well - maybe some stretch tests or something...