Overlapping class C & D

The Dayton Class C airspace sits right next to the Wright-Patterson AFB
Class D airspace. A vector for the ILS approach often takes us over or
through the class D airspace. If we are VFR, I always verify with the
approach controller if we are ok to enter the class D. I have received
mixed answers to this query. Sometimes the controller will thank me for
asking and confirm that the class D controller is aware of us. Sometimes he
will change the vector upon my query. Sometimes the controller has told me
that I am ok to enter the class D airspace as long as I am talking to him.
One controller was even annoyed that I asked him, and proceed to say that I
was ok to transition the class D. What is the normal procedure in
situations like this?