Following on from my recent water pump change due to a leak - Small amount of loss from the bottle and a tell tale pink dribble on the sump and the small puddle on the floor - I discovered a few things about the old(new 5000 miles ago) water pump. A little history first... The car was bought from a garage who agreed to change the water pump and belt as part of the deal. Great I thought .... but I forgot to specify OEM. Never mind I thought can't be that bad and I will do OEM next time.
6 months later I get the small leak and I pretty much know its the water pump so book it in (different garage
and get it changed)
First thing to note is the old pump had the alloy impeller and in fact was just rubbing a tiny bit in the locating well in the head. The mechanic said it wasn't a big deal as the head was cast iron and not alloy but not the best fit. The worst part was that the bearings were shot after only 5000 miles and the leak was from a poorly fitting O-ring seal. The belt and idlers were fine and so the pump was replaced with a VW OEM item. Now I don't have a leak and I am happy I wont need to change it for another 40,000 to 60,000 miles.
So in this case the non VW part didn't do the job and didn't fit well enough. You pays your money and takes your choice. And sorry I didn't get the make of the old water pump - I forgot to ask and have a look