I'm not sure about that Ross, never heard of it
One model pump came with metal gasket and the other rubber
When I replaced mine I went from a rubber to a metal gasket
Darkside developments is probably your best bet, but they're about 250 quid, they do sell gaskets too
I would also try what Darren said, I need to do this too as I have a fuel leak and don't know where from, I think it's from under the car though
Anyway, get it on vcds too and measure your injectors, if the pump isn't holding pressure surely the injectors would read a low value
Also buy both gaskets, then when you change them, you'll know which one you have, thus preventing you from taking the pump off a 2nd time