Mystery leak on my 535i
 

As the title suggests, I've got a leak. Before everyone goes off the handle on oil filter housing and valve cover gaskets, they're in perfect shape and done recently.

Here's the deal:

My new to me 2010 535i xdrive is leaking a little bit, and I cannot for the life of me figure out where it's coming from.

It's on the passenger side, and it drips off of the lower control arm where it connects to the frame. Appears to be oil, or at least similar. Car had an oil change less than 500 miles ago before I got it.

I took off that wheel and removed the bottom parts of the wheel well liner, it looks as though something is dripping on the front axle boot and being flung around while I drive. There's fluid on the boot, on the bottom of the fender heat shield, and along the frame directly below the axle. No obvious leak, but I can't get the car high enough to crawl underneath to get a better look right now.

Any ideas what might leak low on the passenger side? My best guess is that it's oil, definitely not coolant. Only about a fifty cent piece sized drop after parking the car.

No evidence of oil anywhere above the engine mount, just below and away from the engine.

Upper oil pan gasket? I would put some dye in the oil and see what you get.

I checked out the pan gasket as best I could, looks like the leak is further from the block. The cv boot is wet, but the metal on either side isn't. I'll put some dye in tomorrow and see what's happening, assuming it is oil.

Could be, but it's pretty dark fluid and on the passenger side. Do any of the power steering lines run on that side? (this is a US model, left hand drive.)

Went and took a few samples of fluid, big patch is from the leak.

https://cimg5.ibsrv.net/gimg/5series...a7c336d973.jpg
Samples, oil is dark on the left, center large drop is the leaking fluid, and the very clear fluid on the right is from the power steering. Any ideas?

The tricky thing about tracking leaks, is they can traverse from one side to the other. A telescoping mirror and flashlight can be your best tools.

I think dye is your best bet. You should find it quick

I absolutely agree, flashlight and mirror got me this far, which is how I know it's coming from low on the passenger side, somewhere near the CV.

As far as the dye, I'm going to put it in, but it doesn't look or smell like oil, so I'm not sure how helpful it'll be.

This isn't my first BMW I6, and I've checked all the usual places near the VCG and OFHG, no residue from the drivers side or front of the engine, it's isolated to the CV and surrounding area. I'm thinking it may be a turbo oil line leak, but I can't get a mirror far enough down there from above.

I'll have it up on the lift later today and hopefully it'll be a little more obvious from directly underneath.

Reservoir is on the driver's side on this car, can't seem to find any lines that run to the other side and the reservoir is full.