I took at cheap art brush( maybe 1/4") and cut the bristles down about halfway. Then I put a bit of the silicon on the lid where the seal goes and used the brush to spread it out to the edges. It is a thin layer by the time you spread it out. Once it has cured or dryed just put the Unicolor sealing ring back in over top of the silicon. It will be a little bit stiff but you will be able to turn and lock the lid. I then put about 300ml of water into the tank and left it running while I went up and ate dinner and when I came back it was running fine with no drips anywhere to be seen.
I found this tip on the largeformatphotography page posted by GreyOwl who is a member here in APUG, and it worked like a charm.