The sulfur is coming from your engine running rich and having fuel being burned in the cats. Both cats need to be replaced, o2 sensor and MAS Sensor and perhaps the mufflers too. Take it to another dealer and tell them, I dont want my car back till the problem is fixed and be sure to get a loaner. I had the same problem on my 99 S420. As far as transmission, if there is no codes the dealer does not want to be opening the trans up.