Even during the ~8 years since it's been out of service, I haven't bothered to take a second look inside the power section.
I love dangerous high voltages as much as the next guy.
I used to keep an old microwave out in the garage just to put strange stuff into, to see what would happen. My favorite was loosely wadded bronze wool. (steel wool burns). This in addition to many high voltage, high power electronic and mechanical projects.
That said, I have never found a reason to mess with the guts of a microwave oven.