Thanks for the inquiry and for using SearsPartsDirect.com. Hopefully you know the risks of repairing this type of part yourself, especially the wave guide. I would not recommend to use the microwave without it. Read below for the disclosure on microwaves:
I can appreciate wanting to diagnose and repair the microwave yourself, however I strongly recommend against it. We do not give repair information on microwave ovens because they are inherently dangerous to service. Microwaves contain high voltage internal components that can retain a lethal electrical charge even when the microwave is completely unplugged. You need special equipment to work on a microwave starting with an anti-static wrist strap grounded to the microwave to even test components in it. Even minor door repairs and adjustments can cause microwave leakage, and a microwave shielding leakage test MUST be performed using a survey meter after any microwave service.
If you are not a qualified microwave technician or don't have the necessary safety precautionary devices, you may be putting yourself in danger by working on the microwave. If you would feel more confident have a Sears Home Service technician help assist with the diagnosis/repair,
to be directed to the page to set up service.
Thank you for the inquiry and for using SearsPartsDirect.com.