Hi Andy,
Sorry to hear you've got a problem on the tank unit, do you know exactly where the leak is???
I had a faulty in tank pump, but when I done the job there is a large rubber seal in the tank neck, would be worth double checking its not the seal that leaks.
Also fuel hose attaches to the pipes coming through the 'lid' so again checking if the leak is from the hose/pipe joint.
If it's the actual pipes that come through the 'lid' that are leaking/corroded, then probably the only option is sourcing one from a scrap vehicle.
https://www.ebay.co.uk/itm/256067791...iABEgI3gfD_BwE
Bit pricey, but you may find one elsewhere with a good search, some Volvo breakers might be a good start, think there is one Nottingham way, but can't recall their name...
Cheers
Steve