You need a long 12mm ringspanner, and you need to put a couple of bends in it so it curves around the block side of the vac pump.
you also need a puller. the kind you put bolts through not a claw puller.
is it leaking oil or diesel?
degrease it all and go for a drive on a dusty road to see where its coming from, often the power steering burps oil all over the place.
if its leaking diesel you will need to take it in somewhere, if there is oil leaking form where it bolts to the timing plate then just tighten the three bolts and see how it goes.
if you end up taking the pump off, pull the round cover off the front,
put it in 5th gear. push the car along until the Zs or Xes line up on the timing marks, pushing the car in 5th turns the engine nice and slowly.
once the marks are lined up pull the gear off then take it out of gear to stop the engine from moving too far. watch you dont drop the keyway in the sump. the cover bolts are the same thread as the the threaded holes in the gear.
now remove the high pressure fuel lines - a tube nut spanner is best but you can do it with a good quality open ender.
then the three 12mm nuts on the back of the timing plate.
then the secret bracket at the back where you can hardly see it.
now the pump will be off, take it in to get the seals changed, when refitting it you will need to set the timing so its best to leave the old gasket there to help line it up otherwise its a fiddly job.
its not a job for the faint hearted, if you arent feeling very confident about it go buy a gregorys manual...
make sure you cover the high pressure fuel lines to keep dirt out. scrunching a ball of alfoil over them works well. and make sure you degrease, clean and dry it all before starting...
Best spot I knpw of near you to take it is Diesel Central.