Advice on Kingfisher fuel pump

[afarmery]

I'm getting round to fixing my newly acquire Kingfisher.
I dismantled the pump and was surprised to find it was factory painted on the inside, including on the 'wet' side of the diaphragm. Not surprisingly, the paint had melted by having sat in petrol for years, and was gumming things up. Is there any reason why BS painted them inside? I plan to strip it.
The diaphragm was a bit distorted and brittle. They seem stupidly expensive to buy from Sheridan (£10, and more expensove than Sheridan's replacement pump housing!), but I've got no choice. My question is, should I be avoiding E10 petrol in the Kingfisher? In the classic Seagull there's nothing that E10 can rot, but in a motor which has a fuel pump, it could be different?
Thanks for any advice.