I just changed my 3rd timing belt on my 2004 BEW TDI Jetta. 40,000 miles after changing the 2nd TB, I developed a coolant leak coming from the water pump. When I removed the pump, the leak wasn't coming from the shaft seal leakage hole, it was coming from the o'ring seal between the pump body & the engine block. I was curious to see if they recommended using any silicone sealant on the mating surface (it actually said to use the sealant enclosed with the pump, but there wasn't any); but what I did find in with the instructions was a note that the design of the original pump casing had been changed slightly, and that a small piece of the back plastic cover in that protrudes into where the back of the water pump sits should be removed (this piece can easily be cut away with a dremel). The bottom line is that this small piece of plastic can prevent the water pump from seating properly. My car didn't start leaking until it started getting used as a rural postal vehicle and was being used on a lot of bumpy gravel roads. The other issue that I had after doing the 3rd belt was that the small vacuum line that goes from the tandem pump to the brake booster (this also provides the vacuum to operate the turbo vanes & the EGR valve) cracked such that the car started & ran & idled fine, but couldn't make it up a hill. Luckily, I had read a post about this happening & that the point where this line cracks often cannot be seen without removing it.