Original key part number was 776586 as found underneath the the rim of the broken key. It's known as a compactor key, or a key-knob, but in layman's terms, I would call it the "off-on-start" knob. The replacement part number was 386676, and fits perfectly. The original key had become old and brittle, and eventually just broke apart. This was a 30+ year old Whirlpool Trash Compactor key. I just picked out the bits of the old broken key with needle-nose pliers and then easily inserted the new key into the opening. Note, this literally works just like a key you would insert into any lock. It doesn't require pushing to "snap" into place, but once inserted and turned to the "ON" position, locks into place. No forcing is required at all. The new key looks exactly like the original and is working very smoothly.
Trash compactor started making "bumping" sounds when the RAM went through a cycle and tried to come back up. Finally, one day heard a "pop" went the RAM traveled to the bottom. The gear broke in half. Purchased the gear parts "KIT" online and repair took 15 minutes. Easy to do. Unfortunately, this was not only problem. The "cause" of the gear breaking was the Momentary Start/Stop Switch was bad. It's failure led to the main switch not working. The unit could not tell when the RAM had reached the top of it's cycle. The other problem was that I didn't put trash in the compactor. Suggest HIGHLY to never operate the unit's RAM mechanism without the compactor being at least 1/2 full per the instruction manual. Running it empty can cause a major problem, such as the gear breaking/stripping.
Remove two screws from panel above trash bin. Remove panel and remove wires from rotary switch. Remove lock ring from switch. Install in reverse order.