Well, it's up and running again now with a Bosch module
Yep, it was the only option I could find that wasn't explicitly Chinese. It even came with a two year warranty.
The downside is the price and the fact that I could only find one in the USA so I had to wait a week for shipping.
If the pump is just dumping fuel back into the tank from the regulator on the top then I guess that's the return line. It'll just be straining the petrol again, and again, and again..... I'm still curious as to whether the lifetime of the pump could be extended by switching it off once you change over to LPG.
Simon, you're right that the wiring is pretty low quality but I was getting 12V where I was supposed to so I went for the new pump.