Starter Grind On Start-up - a closer look

I have had a grind issue on start up at cold temperatures. Right after the engine starts, I heard a loud screeching sound similar to turning the key for too long. This issue only occured when the car cooled down for a long time (like starting it first thing in the morning).
So I replaced the starter and decided to disassemble the old starter to attempt to figure out why it grinds in clod temperatures. In short, I think it's pretty clear that it's the solenoid.

Ready to be taken apart:


Closer look at the gears inside. Normal wear and tear, teeth are still good (on all gears). Surprised to see them in good shape.


Looking at the rotor, brushes, housing. Nothing out of ordinary, everything is good!


Taking off the solenoid:



Solenoid seems to be working well. But as you can see, there is some wear on the sides of the piston, showing something is not right.


I put it in the freezer for an hour to duplicate the cold start condition. After trying to compress/release it a few times, I noticed it produced screeching noise, as well as hesitation to pull back. So I believe I found the problem here...



Note that when starting a car, the engine relies on the starter to immediately pull the gear away, and if the solenoid hesitates at all, it would in fact produces screeching noise forcing the gear back into the starter housing. Also playing with the gear that engages with the flywheel has made me to believe that even if solenoid fails completely, the rotation of flywheel would force it back into the housing.