[TourerSteve]

Check for any obvious leaks and repair , but to get a base line to work from you need replenish your coolant ensuring that you bleed from the metal pipe above the clutch housing . Also ensure that your oil level is on the mark so you can monitor that as well .Has your oil level dropped ? or has it actually increased ?
Check the fan operation 106 c cut in and the engine temp on the IPK Then obviously run the car and check for leaks and any other symptoms, then monitor your engine levels and temperatures . Carrying out the above with put you in a better position to diagnose your problem
Your miss fire is only secondary to your coolant loss which potentially could cause you greater problems

As others have said the inlet manifold gasket can be a problem , Usually causing rough running on start up but clearing as the water is evaporated out the cylinders , affects either cylinder 1 or 4 and can tell by checking the plug
But with the age of the cars potentially leaks can be from any part of the system or the head gasket A system pressure test wouldn't hurt to trace leaks Also check your expansion cap

Oil leak at the front of the engine under the manifold can be associated with the oil filter and if a turbo the oil feed pipe , return pipe ,also oil can leak down from the cam cover or externally from the head gasket particularly if an MLS gasket fitted
Have you any record of the car having an head gasket ? The cam belt date could be a possibility