I had the exact same problem with my Mara X, and ended up just buying and replacing both valves (cost me around 35€). In my case, it was the safety valve.
Definitely worth it, I put it off for months and just lived with having to dry the drip tray every 30 minutes. It’s a relatively inexpensive and easy fix.
Clive Coffee suggests pinching the tubes that are connected to those valves to find out which one is the culprit. I didn’t notice anything while doing that, but maybe it’s different for you.
