V230 radiator hose pipe comes off
 

I've had 7 incidents of the radiator hose pipe coming off from the bottom where the jubilee clip secures it. Have taken it to Mercedes dealer who have checked for air locks and replaced the thermostat the second time round yet it keeps happening. This only happens at lower revs, like when Im sitting in traffic. When the temp rises, the fan usually kicks in at about 100 deg Centigrade and cools the engine to about 80. but after about 5-6 times it happens all over again. This doesnt happen on long distance drives for obvious reasons
Any suggestions? Has anyone had this experience?