DIY....If the tech is "worried" dont take it there FFS.
I and Doodyrev have fitted 4 cat-back exhausts in our ownership of our zeds and its a piece of cake, 2 bolts hold the back box on and a couple of rubber hangers which are a pig to get back on, apart from that EASY......
Bring it to us, we will do it for a few sheets.
PS its not a gasket as such, its an O ring gasket.