Okay, so I pulled the cap on the low side, it looks nice and clean and dry. When I pulled the high side cap I can see tiny bubbles coming up from around the black plunger.

Is there anything I can do to fix this? It's not a normal schrader valve on the high side...looks like a black bubble blocking the way.

Would a good o-ring in the cap help to hold back the leak? I know there is tons of pressure on this side.

 

there should be a rubber gasket on the inside of the cap...

 

Thanks for the quick reply. I'll head up to the auto store today and get a new cap with a o-ring...the old one doesn't look like it has one.