Is the "o" ring on the drain plugs a size 013-Buna n? I can't believe the dealer wants $2.00 apiece for them, I can get a bag of 100 for $3.50 at Grainger!
In the oilfield diving business we get real familiar with these lil suckers. For these drain plug applications any neoprene "O" ring that is near as damn the same size as the one that came off, is gonna work just fine. I don't pay up for fancy assed spec'd out rings or illusory color coding. "O" rings do like a film of silicone on em, (no matter the application), if you have it. If not, on an oil plug, don't worry.
Also, if the old one isn't nicked or deformed or brittle, and you don't have new one at hand, they're quite suitable for re-use. If you're correctly buying em in 100 pce bags for a few bux though, just change em, of course.