When I was a kid, conventional wisdom was to add 1 quart of ATF to the oil and drive the car a few miles before an oil change. I don't know whether that actually worked or not, or whether it hurt the engine. My first vehicle was a '49 Chevy pickup with a road draft tube, so sludge was a bigger problem back then.

I know that many on this forum like SeaFoam. I used it to soak the EGR system from my '91 245 overnight and it seemed to help a little. Can it be run in the oil for an extended period, or should I add it just a few miles before the oil change? How much do I dare add?

Any other recommendations?

I just read something that suggests that the cold idle problem on my daughter's high mileage BMWs is caused by oil sludge in the VANOS system. This is consistent with the fact that one daughter complained yesterday that her cold idle problem got much worse immediately after we changed from synthetic oil back to 20W-50 GTX, the oil that I used for the previous 200k miles (I got a slew of oil leaks when I tried Mobile1 in my BMWs and Volvo).