ask to see the mech,, let him know you know about the car and most will be happy to do what you want done ,as it means less work because they don't have to trouble shoot it..
when i take my car in for Chrysler max-care ext warranty ,i always see the mech and tell him what is wrong and what it needs he then says ok i fix that today. then i give him $***.** ( money talks) and i get my car fixed the way i want it. My dealer is so good at working with me that Randy wants to bring his and Ashley's to my dealer. jim