I used CN90 tips and trick on my own E39 528 oil leak at the oil filter housing/alternator bracket. Easy job just a bunch a bolts and nuts.

The trick I found helpful was the longer wrench sold on ebay as the BMW one is real short and I could not get any leverage. With the aftermarket one is was simple. The job takes approx 5 hrs including setting up and cleaning up.

+1 on the regulator and then the new alternator. Any auto parts store can test your alternator to see if good or bad.

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green