I have a C240 which had a oil leak but has been fixed and I replaced the fan belt but was getting ignition problems (told it could of been oil on spark plugs) and my garage suggested it could be spark plugs so I had them changed today, it was tested and seemed ok, it did not start untill third time at garage but told petrol needed to get to new plugs. he stop and started a few times and it started everytime.
I have figured it out that if you leave the key in and turn off and on it starts first time but if you take the key out then put it back in it will not ignite the first time, Has anyone got any ideas????

 

the oil leak and belt have nothing to do with your starting problem