I had exactly the same problem, just a trickle of water gets in between the battery and the main body. Initially I though that the battery lever was not putting enough pressure on the o-ring and some water would get in with the pressure [it is so small that you can leave the strobe in the bathtub for a week and there would be no signs but when you go down...]. I exchanged the battery with another one and apparently had nothing to do with the battery, it was always the same strobe, independently of the battery pack.
Strangely the water does not seem to come in through the battery pack lever shaft, neither through the TTL/power dial, there were no traces of water making contact with the tracks in the pcb board where the mode dial makes the contact [and if it was leaking through here there would be], but there was always a minute amount of water trapped inside the main body of the strobe. I honestly do not have a clue where water was coming in, the front assembly was a prime suspect. I removed it, checked the o-ring and re-assemble, I took off the external rubber protection to check if the o-ring was properly seated, it seemed ok, still roughly the same amount of water would get in. There are a couple of things I should mention though, the strobe started leaking some time ago and then it got bumped by the tank of a fellow diver at the surface and the leaking increased substantially until it short circuited the electronics within, no external, visible damage was apparent. I just noticed some airline cracks along the body near the power dial but the dial itself was not damaged... I am not sure what caused them. Also this happened to my most recent strobe, the old ex-1xxx sn was fully working after yaers of service [and I am not that kind to them]. Some pictures attached...
Maybe Ike himself can shed some light on this issue, I am sure they know where the problem lies rather than my ad-hoc assumptions.

