so i've lost a seal 3 times on my 75 gallon. i should have done what theMeat describes above, but i took the very easy route. i drained down to the line it was dripping, taped off the area to spread the silicone, and i used GE silicon that doesn't have the mold inhibitor stuff in it. i've done it three times...so that may be an indicator on where you are headed in the long run...but i did not have the time at the times it happened to me to do what he describes above. i put water back on the joint after 3-4 hours.
again, the correct way - what theMeat details. but if you are in a pinch on time/labor - drain down to your leak point and caulk it, let it sit, and refill.
lots of fun- but if you ain't got a leak somewhere/sometime, you ain't got a tank
good luck