Hi everyone. After nearly 4 months I am inching closer to getting my FD back on the road after swapping in a new engine. One of my side-chores was having the oil cooler cleaned and refurbished while the engine was out. No good deed goes unpunished, and now I cannot find the correct crush washer to go between the thermostat and the oil cooler. Keep in mind the radiator shop pulled the thermostat out, which I wanted, but there wasn't any pieces returned to lead me in the right direction. Maybe this is actually an O-Ring?

I have tried the following part numbers (both shown in the photo below):

N3A1-14-702 - Fit the part, but interferes with the body of the oil cooler causing the washer to be off center. I could grind a bit off of this and make it work. Same part as what goes between the oil cooler line adapter and the oil cooler.
9956-42-200 - Looks like it would work perfectly...except it won't go over the threads of the thermostat.

If I didn't know better it really looks like an o-ring would go there especially since the hole on the oil cooler has a tapered piece...

Thanks in advance!