If it's leaking from the high pressure pipe where it's connected to the pump then it's more likely to be a cracked pipe than a fault with the seal - 'nipping up' will only have any good effect if that union is very very loose because it's the pressure forcing against the seal that makes it seal so well.
If the pipe is starting to crack here then nipping up may break it anyway - this pipe should be fitted with 'P' clips to clamp it and stop the vibration from the diesel engine putting stress on that union by vibrating the pipe - it seems that some mechanics replace this pipe and don't bother replacing the P clips which means the pipe will tend to break again (I still need to fit them on mine
)When this pipe breaks at the union it will dump most of your LHM on the road within a couple of miles and it can easily spray it onto the exhaust pipe - it's a petrochemical oil so it is flammable (though I got away with it when mine went).
Let's hope it's a return pipe - best to find out as soon as you can just in case it's the HP pipe. Good luck.
