The CAT oil filter and adapter that some use on 01-19 GM Duramax engines has some shortcomings. The CAT filter was designed to function vertically so it lacks an anti-dran-back valve. When they are mounted on the Duramax its angles horizontally. Without the anit-drain-back valve, dirty oil flows back into the internals every time the engine is shut off.
If you had installed the CAT adapter now you can now easily switch back and get superior filtration with the PPE Premium High-Efficiency Oil Filter using this OEM adapter replacement. The PPE Oil Filler Adapter works with the brand new "ordnance-style" Special Issue Premium H.E. Oil Filter (114000560) and the classic black Premium High-Efficiency Oil Filter (114000550) for the GM 6.6L Duramax. If you have not installed the CAT adapter the PPE Premium Oil Filters thread right to the stock mating surface. No adapter needed.