20 years old? Spring for a new one.
That is, if it IS that old. The HE was the 1985 version of that toilet...the HF has been around almost that long, but is still the current version. So if I were you, I'd give Groco a call to find out just how old it is...I'd do it on the boat from your cell so you can look for the identifiers that indicate how old it is while you're talking to 'em.410-712-4242 Ask for Pat...he knows everything.If it does turn out to be more than about 7-8 years old, replace it...And make it a Raritan PH II if you want it to last that long. None of "budget" models are made anywhere near as well as they were 20--even 10 years ago...you'll be lucky to get 5 trouble-free years out of anything cheaper than the PH II.