4th gear thrust washers

[Bruce2]

I'm working on a trans that uses a 10 tooth first. The mainshaft is the circlip type, not threaded. This trans is ahead of a fairly stout 2275. The original trans builder welded 3rd gear but not 4th. So guess what happened to 4th? When the synchro cone spun, it lifted off the gear, taking away all the axial clearance. This destroyed the thrust washer and chewed up the gear. The type of thrust washer installed was the one with two notches below. In my parts stash I also have the ones with lots of radial grooves. The ODs and IDs are the same. The two notch spacer is 3.0mm thick while the multi-radial grooved one is 2.8mm. It seems to me that they should be interchangeable.
Will it cause trouble if I use the wrong one?
Which one do you prefer?

I surveyed four Bentley manuals, and they all show the two notch washer for every application, including autostick.
Why are there two types?
What was the intended usage for each?

[Casting Timmy]

I've only seen the 2 oil grove one in my area when taking apart 6V boxes, and the later one was a lot more common for my to see in 12v swing and early IRS.

The one with all the radial lines I'm used to seeing fail in street buggies a lot by first starting to go convex and then eventually it breaks or the plastic cage explodes in the bearing from heat and then gears/ thrust washers break. I mention this as it's confusing to me in the failure with those guys as you think the lighter vehicle weight would be easier on 4th.

My crazy thought is if you had a bearing like the 091 with the thrust built into it could you cut a shallow oring grove in the thrust of 4th gear and lay ball bearings in there. My thought is the ball bearings would eliminate the friction rubbing heat that melts the plastic mainshaft bearing cage and maybe reduce the heat generated in 4th as much too.

I do think the 6V feels thicker which I like, but still typically use the radial kind in favor of more oil in this area.

[Bruce2]

My first thought was that the spacer with 2 notches was what was used with the mainshaft that was threaded. And that the one with multi radial lines was for mainshafts with the belleville washer and circlip. This may be true, but the Bentley manuals show only the 2 notch spacer with the circlip mainshafts.

Since the 002 mainshaft's 4th gear spacer also has multi radial lines, it's my assumption that the left side one in the pic above is the latest version.