clk auto problems

I have a 2.7 diesel, clk  (03 - 50,000 miles ) which loses power in auto - almost as if the gears are slipping. Then on another occasion there is no power at all.  The dealership replaced the valve block at a total cost of £560 but the car broke down 100 miles later with same fault. When Merc technician came to the call out his diagnostic kit said "no fault present".  Car wouldn''t move... then when he called for relay truck, I got in the car and it drove around the car park.... frustrating or what  ??

its a mechanical fault this models ave alot of troubles firstiy you need to have a GLYCO TEST this checks if the atf as any contamination which most proble it as, this is when coolant travels in to the box and wears all the brake bends,so when the engine temprature reaches 80deg it stars to slip like there is no power suprise suprise the dealer u went to are not aware...........

Naz, thanks for your reply.
Should have mentioned that when i picked it up after the initial "repair" they did mention that they had done a glycol test.  It was after that that they replaced the valve block... but the fault is still there..
Even when it does power up (only for a short time and intermittently) it doesn''t sound healthy !

Latest from dealer is that the car needs a new auto gearbox... cost £3900 !!!  Ouch!
Shouldn''t need this in a quality car that has done only 50,000 miles.
Dealership talking to Mercedes Benz about them "making a contribution".  Let''s hope it''s a big one !