I also believe the intermittent water at the bottom is probably condensation, cause once a tank starts leaking, it doesn't stop. On the other hand, I had a rheem with the round plastic drain valve and evidently after draining it one time, the nipple cracked going inside the tank. It just leaked when the tank was heating. I thought it was condensation until the outer cover starting rusting below the valve. Took the valve off, saw the discolored crack in the nipple, and put in a nipple and ball valve which fixed it.
I couldn't see the leak cause of the tank cover so I wouldn't rule out that the drain valve or the T&P valve could be leaking. You may try taking them out and doping them up. Eyeball the conections on top to see if they can possibly leak.