I installed a new fan and clutch last summer (sachs) for my 300D '87 (124). It took me a good driving in a hot day to actually make the fan clutch starts locking and it did good job since then. It seems that these clutches are stored horizontally, which is wrong according to MB CD. The fan clutch works with a valve that opens using a pin, I think this pin can be stuck untill the clutch is USED hardly. My advice is to make SURE that the clutch is engaging, before anything else, it makes all the difference. you should hear the fan roaring at the start (cold) and when revive the engine at idle when it is hot after driving.