Here you have a brand new CL01-12 high voltage diode which fits between the capacitor and the microwave chassis.

This particular diode is usually paired with a high voltage fuse which sits in a plastic holder on the transformer output which will blow if the diode fails so you'll need this fuse too.

Picture 2 shows the circuit diagram.

Lower power microwaves (less than around 850W) may have a 650mA fuse

 safe replacement.

Fuse dimensions: length 40mm, diameter 6.5mm.

(Check my other listing or contact me if there is a second diode across the capacitor terminals rather than a fuse)

**** Microwaves Ovens are dangerous. The capacitor can store lethal amounts of high voltage energy even when the oven is not connected to the mains, especially if there is a fault. Leave the power cable plugged in but turned OFF to maintain a connection to earth. Ensure the capacitor is discharged by touching the terminals together and to the chassis of the microwave using plastic-handled screwdriver or needle nosed pliers before touching any connections in the high voltage circuit ****