Jase we have fitted loads of them, Sometimes the impellar come's loose so they loose preasure and other time's they get noisey and can keep going for a while till they stop. Could be 3 years, could be 3 days. The only sure thing is one day it will stop so may as well bite the bullet and put one in, Save getting stuck somewhere when it does go. The early one's were real bad, the later one's seem a bit more reliable but still not great.
There are actually two pumps in that unit. A low presure one that pumps fuel up to the filter head then back to the pump wher another pump then pushes the fuel forward to the pressure reg on the head at a second higher pressure so it aint as straight forward as just fitting a pump the the fuel tank unit which is probably why none of the fuel parts type companys have produced a replacement yet.
When you refit it you can make the pump "purge" the system by turning the ignition to the second possition then pressing the accelerator right to the floor and releasing it 5 or 6 time's. The Engine management light will then start to flash and the pump will run. Leave it run till you hear a noticable change in the sound of the pump (1-2minutes) then you should be able to start the engine!