Pretty sure the Motorcraft FL-1995, uses a spring for anti-drainback. 2000 miles on the change (done early to investigate, WMO goes back in as fuel). Oil cooler does have a small leak... but the recovered pieces have small ridges, inconsistent with a rubber o-ring
You are correct. A search showed me that while the FL820S and several other motorcraft filters have red silicon ADB valves, the FL1995 does not. It really does look like a molded plastic part. I'm not real familiar with the internals of this engine but it doesn't look like an umbrella seal I've seen before. Found an umbrella seal keeper in a BBC one time mashed between the oil pump gears. Not where you want to find them. Twisted the cam. Trashed the distributor. Lots of badness. Luckily shut down before any major damage to the rest of the rotating assembly.
I have seen rubber orings mashed into funny shapes before, but I don't think that's what you have here. silicone from inside the pan where it's been off and replaced? Was it hard or rubbery?