Here's my suggestion. Take your car to the dealer and complain about the lag in downshifting. Tell them that a friend of yours with a 98 CLK had the Transmission Control Unit replaced for a similar problem...and ask if it is the same unit. I know that 98 E-classes and CLK classes share the transmission, but I'm not sure about the '97 (I know the engine changed to V-6 in 98). My dealer really didn't argue about it at all.