For the first time I saw the low coolant symbol light up on the display. Checked it and yes it was low (slightly), topped it off about a week later same thing. So I start to look around, found coolant weeping down the passenger side top of radiator - like the edge seam of the tank and core. Not sure if it a repair is possible. Looking around at prices (ECS Tuning) lists the RS6 (4B3 121 251F) $1371. I checked the p/n of the regular 4.2 C5 - it is 4B3 121 251D for $548. Are they not the same ? Usually the last digit is a revised p/n. Anyone had to replace theirs ?? Options ??