For your rev meter check the connector on the back of your alternator as that's where the feed comes from! As for the leaks so long as your coolant pipes and rad etc are ok the other place you often get leaks on 300tdis is at the p shaped gasket between the water pump housing and the block, if you look in the engine bay from the passenger side behind the alternator you may well see a rusty streak where the water has been escaping. It isn't too bad to fix so long as you know which bolts need undoing and which don't, you'll need to take the water pump pully bolts out before you take the belt and the tensioner off as the belt offers the resistance needed to undo them and also if i remember right there are just the 3 bolts on the front of the power steering unit and 1 on the rear to take off to get that out of the way. aside from these just keep taking things off until you succeed but don't forget the nut hidden behind the tensioner