A855 - 5 Speed

So....once it goes into gear, there has to be a significant 'something' causing it to go back out.

It would sometimes go into gear and stay.
The vast majority of the time it would be in gear but you could tell it wasn't. Then just wait and pop, sometimes fast, sometimes slow, but never related to speed, rpm, acceleration, etc.
I posted a video from under the car, putting it into gear with a wrench, and it would click twice. Turn the crank, and eventually find a spot that seemed to be in gear.

I don't recall reading if the trans would stay in gear IF the shifter was held in place? And if so, could the driver feel it trying to pop out?

Hold shifter in place, it would stay, let go and pop.
After a year, I started to believe I could tell, with some accuracy, when it wasn't going to stay, right when I shifted into 4th.
However, I was accurate because it just wouldn't stay.
Harder to tell when it was going to stay.

To clarify, again, it popped out for them as well, both times it went back, as well as the other trans in their test car, twice.

I posted another video without the boot and it made a horrible noise in forth, especially when holding it in gear.
Also a strange sound in neutral.

One of the last rides the kid and I tried to guess when it would stay or not, iirc it stayed once and the reality is we always guessed it wouldn't.
It became too frustrating and I skipped 4th on the way back.

It was at times a heck of a thing when it popped, so you didn't want that.

Thing is, I realized how dangerous it was driving around with the focus on the shifter and not on the road.

It seems many on here are constantly thinking, questioning, trying to figure it out, but those who continue to sell it aren't interested.

Why would machining the case be an option to attempt, make any difference? And why would it not be needed for any working trans?

Why would a 'heavier' side cover spring make a difference, why would they even think that?
Why would they want to send me a new side cover with the new fancy spring when it's easy peasy to just pull the cover and remove the spring?

These questions are as meaningless as the answers.

Look back at the emails I posted, consecutive emails with no logical flow whatsoever, ignoring their own data and testing results.

I talk too much.

To borrow a line, with a slight modification:

At least you know that "<insert anything on this topic>" means absolutely nothing.