Since people on this board have stating that WM is closing out M1 filters for $7. I stopped by my local WM to get a few. Well, the WM in my area did not have M1 filters on close out - they were priced as they have been at $7.97. Since Autozone charges $12.99 and PEP Boys, $10.99 for M1 filters, I went ahead and picked one up. I would have picked up 2 but the only other M1 filter they had for my application looked like it had been installed and then removed from a car and the can was badly dented in 4 places. WM did not have the oil I was after so I went to PEP Boys. PEP Boys had a display of the new RP filter. Looked up my application and they had the filter I needed for $14.99. I looked at the filter and it is identical to the M1 except the RP has a purple antidrain back diaphragm. Do not know who makes the filters marked ZZ on them but, as stated, the RP and M1 are identical down to the location of the ZZ. The AC Delco for my application is also stamped with ZZ but the holes are a different size (larger) then the RP and M1 filters.