So last night I started to process some film and realized that the tank I usually use was still damp. So I grabbed another from the shelf over the sink and loaded it up (using my latest dark box of course.)
I filled it with SP-76EC, squeezed it and started agitating. It dripped. I re-squeezed. It still dripped. I thought about putting it back in the dark box and swapping lids but it wasn't leaking that badly, so I kept going.
I figured the O-ring was worn out since it was one of the very first tanks built. (Kind of surprising since that particular tank didn't get used that often.)
Anyway, when I removed the O-ring, I had an oh yeah moment.
Notice how the O-ring isn't round but has memorized the shape of the lid?
So I rotated it 90 degrees and reinstalled it:
I filled the tank with water, squeezed it and turned it upside down. No leaks!
Now we can't guarantee that just rotating your O-ring will fix every worn O-ring but it can't hurt to try it. You can also wipe it down with a touch of silicone lubricant.