Filler neck - metal ring corroded - new fuel tank?

Hi,
Has anyone dealt with an issue like this before? My mk3's metal ring that goes around the filler neck and allows the fuel cap to locate has corroded so much it fused to the cap and has disintegrated.

I can't see on the parts diagram that this part is available so is it really a case of installing a new fuel tank??!

Last pic is of my corrado where the metal ring is present (but also corroded actually).

Thanks
Matt

 

I've got a kaput mk3 tank I can lop the neck off matt if want it, not sure if can swap collars, but here if needed pal.
Could you remove the old one from your tank by breaking it up as its half off already, then remove ring off scrap neck with heat/burn it carefully and then reinstall on yours by compression or bonding?

Could that be my third 'moment'?

 

Cheers Dodgy. I've been chatting to Leo the mk3 breaker on facebook and he's sorting me a tank for a very reasoable price - costs more to post it!

However that said I would still be interested in it I think as i could use it on my Corrado? I'm pretty sure that would work as the cap is the same. I'll have to do some research before you go butcher mode

 

Let me know, I'm getting a new hacksaw for Christmas.
Tank has a hole in it, so when get chance I will strip and dispose of it.
Vaseline around the cap and collar, guy at the old school petrol station near work suggested it as our cap sticks to seal on the green one and my wife can't undo it to fill up.

Lucky to get one sent, I've had to collect all the tanks I've bought.

 

Error

 

Rubjohnny this is for my mk3, it's just my Corrado one doesn't look that much better!