If you really want to do it, I would use this;

Products - MotorClean


I think Weasel says he has used the BG products at the dealership before. I am not sure which exact BG product it was. My guess is the Quick Clean.

BG Products, Inc.

I used the Liqui Moly motor clean in my high mileage e36 a few months back. You add it to the oil and run for about 10 minutes, then immediately do an oil change. My guess is that the BG product is used the same way. You can also just do a couple quick oil and filter changes after a few thousand miles. That should help clean thigs up as well.