I replaced the bottom O-ring with a new OEM one last year when it appeared to be leaking. Now it appears to be leaking again, if it ever stopped. The picture shows that the solenoid itself is fairly clean, so the top O-ring is good. I've cleaned a little underneath to verify and should be able to confirm in a few days. Has anyone else had trouble getting the bottom solenoid O-ring in properly?

Another option is the distributor O-ring, which I replaced 2 years ago. I'm not able to tell which one the leak is coming from.