David,

I am no expert, but if it was me, I would first soak it in vinegar first, like on gallon of vinegar to 10 to 20 gallons of clean fresh water. Let it soak for a couple of days. Then scrub it with a hard bristle brush. Then, dump in a few pounds of baking soda and add water to fill the tanks. Let that soak for a few day and see how that works.

Then stop at a Home Depot or place like it, get more gasket material and make new ones.

It may not require re coating??? Also, make sure you draw some of each mixture through ALL of the lines. They can also have junk in them.

Just a few ideas....

Greg