Update:
I had to replace my tires for a couple reasons... first, I had this puncture on the edge of the sidewall (it actually happened about 3k miles after I got the tires; I was so pissed) that I plugged 3 times until it finally got to the point where it would lose all air pressure overnight...
... plus the car began pulling to the left even after I had an alignment done, and I've just gotten sick and tired of Dunlop tires. I wasn't too happy about the prospect of replacing four tires with 6/32nds tread left on them, but I got a set of Kumho Ecsta LE summer tires for a really good price, and Kumho is also currently offering a $50 mail-in rebate on a set of four tires.
However, that was not enough appeasement for the Subaru gods, who saw fit to cause my pumpkin cover to crack:
I started having seepage, so I put Teflon tape on the drain plug hoping that would fix it, and as I was tightening it, I heard it crack. The drain plug never felt like it was getting any tighter, so I think it was weakened, which I also think is really why it was seeping.
So I got a new one (thankfully, all R160 pumpkin covers are the same, so I could have even used one from a Datsun 510 if I wanted to), and had an absolutely wonderful time dropping the rear diff to replace it.
Fixed.