This post is confusing. You say the radiator doesn't "vat" the tank. Are you saying the shop won't clean the interior of the tank?

If they clean the interior then coating the tank is not required. You can do it if you want but coating is usually used for a "seeping" type of leak.

If the interior of the tank isn't boiled/cleaned then the rust won't be removed. Any rust will indeed find its way past the fuel filters and into the injection pump. The existing filtration system will only catch particles above a certain size. Finer particles will pass and enter the pump/lines/injectors.

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