Good to hear you solved the problem. Those "O" rings are a PITA. I would always be very careful removing filter cover, examine "O" ring carefully and if there was no visible damage, dip my finger in Hytran and rub it on "O" ring and carefully replace filter cover. Only replaced "O" ring about every 3rd time.
The only "O" ring worse was the oil filter canister on BD-154, had to look upwards while oil dripped on your face!!!