Paul:
The only resolution on the trans from MBUSA was that they support their dealers and area reps judgement and decision that they will an intermittent failure is only real if it happens when they see it, but they will 'consider' goodwill repairs 'within a reasonable time frame' if they ever see it slip or if it fails.
The dealer is refunding the Heritage extended warranty I purchased on their recommendation to specifically cover the trans (for issues they now say aren't covered!). I am going to set aside the warranty money as a trans repair fund, and will be back in their face each time it slips for as long as I keep the car. If it resumes slipping, that may not be for long.
On the brakes, thanks for the info, Yal. I wondered about doing the C280 rear rotors as well as the fronts just to get past the proportionig valve issue. The C230 has a vent in the front bumper that goes through to the wheel well in front of the tire - I assume it is for cooling but I suppose it could be an air pressure balance type of vent to reduce wheel well turbulance. It shouldn't be hard to extend this around to add airflow over the caliper/rotor assembly.
Phil in Fastlane told me that the C280 brakes would be an expen$$$ive conversion, but that they carry an ATE VENTED power disk rotor for my model, which would solve my problem. He said the parts chart said they would fit, but to double check with MBDoc or Donnie. I'll email them and see what they say.