why do they say its the rail?
the easiest way to fix this is to remove the inlet manifold and all the injectors and then re-fit. to ensure all the injectors are correctly seated get 4 new injector o-rings from gsf for about 20p each. failing that if there is a running problem though it could be the injectors themselves.
if this is the case there is a place in holbeach that can clean them to ensure they flow right failing that they cost about 30-40-50 quid each brand new. i bought some a few years ago but cant remember exactly how much i paid