Just my two pence worth - I had a similar issue the BAS/ESP light came on and off intermittently without affecting any other systems. I screened my car with my Autel scanner, and the live data showed the yaw sensor was showing constant variations in degree angle even though the car was park stationary with the engine off. I replaced the yaw sensor (part number A0025428918 version 01-05) which is located between the gear stick and the handbrake in the cabin. The part was second hand from a Mercedes ML 270 Cdi W163 and cost me £18. Scanning showed no more variations in angle when parked, and the light has been off for the last year or more!