Check your tranny fluid-a cracked tube in the cooler section of the radiator will allow the coolant to mix with the tranny fluid & destroy the tranny. If the tranny fluid at the bottom is milky you've found the problem.

__________________
87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)