You drop a tool in there? Use a torque wrench to tighten everything? Maybe a bolt came loose? Any codes? Did you inspect the chain guides that were visible? I also seem to remember certain n52's having problems with the cam gear bolts sheering or backing out.

I doubt the sludging is the problem. Here is what a 182,000 mile n52 looked like last year when I bought my E61 wagon. Previous owners were not kind. Looks much better now after some Seafoam and ATF in the crank case treatments. Runs like a champ.

__________________
2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)