Mah Starter Broke (Literally)
 

So, on Saturday, I left work for lunch. When I started my car, I noticed it sounded a little different from usual. I turned it off and started it again, and it sounded normal, so I thought little of it. It started fine on the way back from lunch as well.

When I went to leave work the starter made a bonk WHIZZZ noise while starting the car, and when I shut it off it would not start again. Some coworkers gave me a push start, and I hightailed it to an auto parts store to check the battery and alternator. Battery at 330/340 CCA, good. Alternator juicing at 13.9v, no problems. Starter motor only pulling battery down to 10v (but not starting, just a crank or two and stop). Battery terminals are tight, and still covered in anti-corrosion goop. Well shit.

I roll backwards to jump the car and drive home. I park it and pop the hood, and start checking around the starter. Ignition cable is in good condition. Battery cable is snug on the starter. Starter is nice and tight to the engine/trans. I yank off the ignition cable and slap on my remote starter, hoping that my ignition switch is to blame. Same symptom, one or two cranks, and stops dead.

I decide to let the car sit on Sunday, because I was pretty sure I had a 99 starter from the parts car I bought in storage, which I couldn't get to until Monday. This morning I tried to self push start on flat asphalt (I'm sure someone got a good laugh from that). I wound up ditching the car and taking the bus to my storage unit. Couldn't find my parts starter. Wound up having to buy a starter to install, which had to be delivered from across town. Got back home and started working on it around 10:30. I got the old starter out by noon, and found this.

One of these things is not like the other....
https://www.miataturbo.net/attachmen...ine=1384819847

Luckily, the entire nose was just inside the transmission through the starter hole, barely in reach, so I didn't have to yank my transmission to find the missing piece of this starter. It looks like the new part has a thicker casting in the area where the old one broke. Judging by the label with a big Japanese character on it, I assume my starter was OE. I'd complain more, but I'd quit at 190,000 miles too.

Normally with a failure like this, I'd be worried about my flywheel, but the teeth that I could see before I put the new starter in looked perfectly fine, and the nose was stuck in the little pocket in the transmission, not rattling around. It also didn't look like it was riding on the flywheel, as the ragged edge mated up to the starter perfectly.

What I'm thinking is that the solenoid started to fail, and the starter gear was stuck engaged, but not powered, and I caused the nose to break by driving with the gear engaged which beat the snot out of the shaft and the aluminum nose. Is this feasible, or should I be looking for another cause? Or is it just old age and aluminum fatigue?

Edit: Looked up how starter solenoids work. Figured out that's not possible. Have no idea what caused the failure.