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One Day
Try a deep clean first. T-Cut dries milky on anything.
Can't think of anything that would sort that out mate but like ATS says if it's knackered then you could sort of try anything. I know there is something out there that removes scratches from porcelain toilets and basins etc but whether that will work on glazed i don't know.
I know it's not ideal but any chance you could tile over just that wall rather than taking it all down?
It's a good idea but going from the (reflection) i can see in your photo it don't look like you will be able top extend those feeds, worst case is tile off under the valve and split the pipes lower down in the wall and then run them through again!!! like you say it's a load of work just to be able to then tile over the top. Cant get to the pipes from behind or anythig mate?