The bottom line, I'm concerned about fighting a failing sealant coating "down the road"; particularly on the road.

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Concerns about reliability won out over cost; ordered a new tank yesterday.
Thank you Carl and Jockbolter for your comments.
Bill
I see you've opted for the new tank Bill,like you say it will hopefully prevent any issues along the road and apart from the obvious safety concerns,at least you should also be guaranteed a clean tank with no internal rust/sediment issues.
One less thing to worry about!
I can't remember who manufactured mine but if your new tank has a welded filler neck,i'd be double checking it
before installation just for peace of mind.
Hopefully mine was just a rogue that escaped quality control.