I'm using Titan HD Super SAE40(German oil) since i got my car from 3 years,which is recomended by the mercedes dealer in Kuwait.I tried once Elf semi-syntethic(10-40)which is french oil and it gave better performance and smoother ride but my engine starts to leak(down the oil pan).Tomorrow I'm going to change my head gasket and some other gaskets and seals.So is it safe to use Syntethic oil after i change my gaskets or still it will leak???