Don't have a cow. Aftermarket gas tank sealants are pretty common. You just clean the tank, (shake in some loose nuts and bolts, and shake, shake, and then shake them out) Rinse thoroughly with gas, rinse again with solvent (as recommended by the product you buy). Pour the liquid tank sealant in, swish it around, possibly let dry and swish in another coat. I have used a sealant called "Cream" for years on antique cars and bikes, worked great every time. You don't have to go to a "professional". There's really not much to it. Cost is usually about $20.
