Autotrol 155 leaks at brine refill

I replaced the resin in my Autotrol 155 water softener. After putting the unit back into service, I ran a regeneration and everything looked fine, until it got to the final stage of the brine refill and purge. During the last part of the brine refill, a small amount of water dripped from the back of the unit, from the area of the bypass valve. I can not really tell where the water was coming from, so I don't know if the leak is at all associated with the bypass, it's just that is where the water was dripping off the back of the unit. It was a small amount of water, less than 1/8th of a cup I would guess. There was no water dripping at the beginning of the brine refill & purge stage, it didn't appear to begin until after the water level in the brine tank rose enough for the brine float to shut off the water flow to the brine tank. There are no other leaks when the unit is in the service mode, nor are there any leaks at any other point during the regeneration cycle, only during that final phase of refill & purge.

Any ideas where I should look to fix this leak? Thanks.