Humm... In my case I never removed any of the original heat shielding. I also still have the factory header. I am also de-cat. Finally, it was both the front and rear engine mount inserts. The front is not near the exhaust. <30k miles on the car w/first set of inserts.I've seen some pictures of the 'inserts' melting, something to do with removing heat shields when installing aftermarket exhaust.
Something to think about, and probably easily preventable, too...