3/4 synchro

Here's the deal about the oils, in my experience
The brass rings are brakes. When you disconnect the input gear from the crankshaft, by stepping on the clutch,then all the gears on the mainshaft are supposed to be free to turn faster or slower. Supposed to be. Let's assume the clutch is working properly, and they are free. Ok now, the brass rings are brakes. or supposed to be. When you begin the shift, the fork moves the slider. That motion is transferred to the brass, thru the struts, by the springs pressing the struts into the sliders.. The brass is supposed to brake the chosen gear to match the driveshaft rpm, either speeding the chosen gear up or slowing it down. When synchronization has been achieved, the slider passes over the brass and the clutching teeth engage the gear. All this is supposed to happen in microseconds, as you slam the stick from gear to gear.
That's how it is supposed to work.With a fully disengaged clutch, and gears that are freely rotating.
Now, if the selected oil is too thick, too viscous, or too slippery, it takes more time, and if you are too forceful, grinding occurs.
And if the oil is too thin it is forced out too quickly and clashing may occur as the brass grabs the gear, and locks it between clutching teeth. However IMO this is a better situation than the first.
The cluster pin needs EP protection or it wears out prematurely. However it has 2 or more lives so I never worry too much about it.
Full Synthetic is just too slippery. Some guys use it, to some degree of success, But I couldn't make it work fast enough to suit me. And I really tried, modding my cones and brass with channels to get rid of it, and adjusting my brakes.
And about those brakes. If the brass won't bite the cones on the bench dry, you can bet they won't work installed. The cones have to be deglazed in a lathe with emery cloth to create the bite, and I bias mine to the upshifts, except first I bias to the downshift side. And the rings have to be round! If they rock on the cones they will be slow and or they will be the author of grinding. And finally; they have to sit high on the cones, else the clutching teeth will get together before the brass has done it's job. This is especially important on 4th gear, cuz it is usually a little further away from the slider's parked position in the first place.
And lastly lets talk about those energizer springs and struts. They have to be matched to eachother and to the slider. There are three kinds that will work in the A833; the early style, the late style, and the accidentally swapped in 3-speed style. I prefer the late style, but both A833 types work equally well on the street. Do not use a swapped in transplants from a 3-speed, They are not made to shift like lightning,lol. The A833 ones have long and deep humps on them that you can exploit with extra spring if you need to. Stock works for most. I stretch the crap outta those energizers before I put them back in. IIRC, I put an extra one in the 4th position to push the brass out a lil further, to initiate braking a lil sooner, cuz that gear is out there.

Back to the oils. 100% ATF works fairly well and IIRC was the FSM oil for a few years. 100% EP oils for me have been too slow although 75/90 is pretty good on my modded cones. So I mixed it 50/50 and it worked right away and so I didn't experiment any more after that. Those modded syncros of mine have about 60,000 miles on them now, or more;while I put over 100,000 on the used gears.The brass are older-than-Adam, used ones from the 70s.