I drove a 65 Dart with a slant 6. It had oiling problems once. The filter on that engine mounts upside down and at some point in it's life, part of a filter came out and ended up inside of the threaded pipe blocking about 90% of the area. It was a stainless round with semi circular cutouts on 4 sides, I assume part of a 1 way valve to keep the filter from draining. Anyway I've no idea how long it was there but after opening up the engine, it had clearly been there for a long time. Only found out when the oil light came on one day.