Once my chemistry teacher told me not to use such fancy fuels like hi-octane for vehicles and once you have used hi-octane than better not to switch back to the normal oil it will destroy your engine , as hi-octane has more number of oxygen than the normal one , i will not go deep into this chemistry stuff but better not to fancy your chances with such fancy oils
its mehran don't deal it like BMW , your mechanic is nuts , he has no idea about what he is saying because he don't know the ABC of chemistry , they will ask you to do all the fancy things you can possibly without having a slightest of ideas what its all about . Your mechanic suck big time