Fuel pump seal/\"o\" ring...
 

When I took the fuel pump out of my tank ready to send it away for a respray, I managed to break the big green "O" ring seal.

When I re-fit the pump with a new o-ring, is there anything I can do to make it easier to slide the pump in, so as not to stress/damage the new o-ring? - as I know its a very tight fit.

Am quite wary that I probably shouldn't use any kind of lubricant to help slide it in (oooh er!) as I guess it could contaminate the petrol, once its in use?

To stop the fuel pump assembly o-ring from rolling out of the groove, put plenty of Vaseline around the seal, groove and around the hole in the tank where the seal sits. Its always a little tricky, but this helps keep the o-ring in position. Don't worry about any excess getting into the fuel because the fuel will dissolve any excess Vaseline that gets into the tank.

The o-ring gets stretched when you install the assembly making it very difficult to reinstall. So it's best to buy a spare before you need to remove the assembly.

If circumstances require you to reuse it a second time (even if you break it), use a razor to diagonally spice the ends so as to take the slack out of it 'till the o-ring just wraps around in the groove - not too loose or too tight. After cleaning the ends (with say carb or brake cleaner), apply a little Superglue and then hold the O-ring ends together until the glue sets. Let dry and reassemble.