The 4.8l water pump does not last much more than about 70k miles. The seal starts to seep with the crazy engine temps BMW has this engine run.
My pump started with a slight knocking noise. i think the bearing cage breaks and then the bearings become loose and the race becomes pitted. I started the engine one day before I had a 2500 mile round trip I had to take and heard the noise and just said "crap". Tried to get a water pump from the dealer, they did not have it is stock.
I chanced the trip, pump became noisier and noisier on the trip, but I hoped and crossed my fingers once the engine RPM was up over 2000 RPM that the bearings would redistribute themselves and the pump would last.
I made my trip without a grenade on the front of the engine!
I went ahead and installed the
BimmerFix Products | BMW Coolant Pipe Repair System coolant stent pipe while I had the water pump off.
I also cheated and did not remove the lower pulley from the crank balancer. The bottom bolt was a PITA and tight, but if you have "normal" size hands and fingers and some patience, you should be able to get by without removing the lower pulley.
I also switched over to a Hamburgtech 90C thermostat and have been running this for the past year without problems.