Somewhat related directly to Beech, although the lines get crossed.

My buddy from Botswana had a couple of Curtis P/N CCA-1550 that came out of a Cherokee 140. Nothing wrong with these drain valves except that they were ugly and the seals leaked.

So, he tossed them in the ultrasonic cleaner with Hoppes No. 9 for the time required to remove the layers of grunge. He said it took a little longer on one than the other due to some remnant greenness inside by the spring. Then, he lightly brushed them with a wire brush to restore the luster.

Then, he got some P/N CCA-1319 seals from Aircraft Spruce. Aircraft Spruce says these are "FAA-PMA approved replacement parts to maintain your Beech..." At the bottom of the Aircraft Spruce page, there's application information.

And, on McFarlane Aviation's website, under P/N CACCA1319, it says these seals are for CCA-3400 drain valves. It also gives dimensions. ID 0.015", OD 0.350", Thickness 0.058".

Sounds about exactly what the remnants of the seals on the CCA-1550 were.

These are not o-rings. They're flat seals with rounded edges.