Gearbox Needle Bearing Questions

[Steve Nau]

Keep in mind as you read this that I am a complete novice trying to reassemble my 519 gearbox.
I tore it apart initially to replace the syncro rings.
Put it back together and when we started driving it there was a noise in the gearbox that sounded like a bad bearing.
Took it out and replaced the rear mainshaft bearing. The others looked OK.

Here is the problem.
I discovered in the bottom of the case two needle bearings.
After removing the pinion shaft I discovered they had come from third gear and the bearing cage had a bent prong which is broken off now as shown in the attached photo in the upper left corner.

So ...
1. Anybody have ideas as to how the two needle pins would have escaped from their cage? The first time I reassembled the gearbox (out of five times so far) I then discovered one needle pin laying on my work bench. So the second time I tried to be very careful when I put the pinion shaft and gears back together and back into the case. That doesn't mean they didn't fall out then but I am wondering if there are other possibilities that others have encountered.
2. Why is the brass cage for third gear different from the other gears?
3. How do I determine if the needle bearings need to be replaced?
4. Would not having the correct shims on the shaft have anything to do with this issue? I was under the impression the shims were related to alignment with the differential.

[Jacques Lefriant]

Hi
Steve
1. i call the parts rollers. you may have left one out BTW i see damage to the thrust surface
2. since the pinions(gear with inner races) have different dimensions there are 3 different cages 1+2,3,4
3. by fitting oversize rollers the rollers come in over sizes but must be done by fitting complete sets per gear.
4. you must do the box by the book with the specified tools sorry.
j