ive been in this suitation before and went back to the mechanic and all what happened is that they denied it, so i went and got an engineers report from serveral workshops that are well known and have been in the industry for a while
and went back with my findings only to hear them say the report is bullshit there wrong and the rest of it .......after 6months of fart assing around they decided to fix the problem but did a dodgey job of it and 1year later it blew up again .....
from then on if anyone asks about this workshop i will tell them my personal opinion and tell them to stay away ..
buts its only fair to take it back to the workshop so they can have a look at it first and then go from there ..or from there response......
hope this helps to resolve this problem .