Before you do anything else, try the vinegar. It that sort of helps then use some muriatic acid or LCR like stuff. That may work because the typical fouling is calcium papitate.
Then again, you may have to get in there and really clean it or replace the seal, but they the easy stuff first.
Matt - once a Thetford engineer
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.