Rebuild kits are available, but...
First you need to know which model Groco you have. If it's less than 10 years old, it's an HF...but if it's older than that, it could be an HE or even an HC. About the only way to find out is by calling Groco: 410-712-4242. If it hasn't been used in several years, I recommend that you get the "master" kit for it instead of the standard kit.If it's older than the current HF model, and it needs any parts that aren't in the kit, it'll prob'ly make more sense to just replace the whole toilet...'cuz you'd need an "upgrade kit" in addition to the rebuild kit, which would run the total cost of parts up to more than the whole toilet. Grigs, I don't know why you'd say that Catalina owners are a "captive market"...'cuz Groco toilets aren't unique to Catalina...rebuild kits parts for 'em are available from many sources.