TIP: Make sure the fuel tank is near empty to avoid tank distortion before inserting the pump ring. Ensure the threads are perfectly clean and the new or used pump is correctly located. The pump spring should be relatively weak so very little downward pressure is required. Before you insert the ring without the pump in place, insert the ring into the tank and gently turn it backwards whilst listening for the thread starts 'click' then mark exactly the ring and peripheral mating threads. Then lightly grease the ring and mating thread and ensure a new gasket is installed. Gently turn the lock ring ensuring it's not cross threaded.

I have only once needed to remove the fuel pump to replace the TD5 plastic fuel line that had ruptured (common fault so I reinforced the new fuel line). I have to admit that I had no problems whatsoever with reinstalling the pump but I had drained the fuel tank first.