Probably best going down the route of having a new one fabricated from either alloy or stainless.
The original lead coated steel (turnplate) from which they were originally made is no longer easy to source.
I've repaired petrol tanks quite successfully by steaming them out with a steam cleaner. It does also get the crap off the outside. I still work on them out doors ans always wave my oxy torch around and in the filler pipe stub.
Arwyn
