Why is GL4 OIL so hard to find?

I've scoured through Amazon, Ebay and all of my local parts stores and there is almost a complete absence of GL4 rated transmission oil.
Why?
GL5 oil/lube has additives that damage brass or bronze synchro rings. It accelerates wear by over 60% in some cases. And doesn't have a good drag coefficiency. It's too slick.
A lot of oil out there says "GL4-GL5 Compatible" but then goes on to say that it is NOT to be used in synchronized transmissions!
Most standard transmissions are synchronized.
Does anyone sell a straight cut geared, non synchronized transmission?
So why is it more or less not available?
I found VALVOLINE Synchromesh oil. It actually claims to be GL1-GL2-GL3 and formulated for synchronized transmissions.
BUT it's a super light 30w oil and probably not up to the workings of a truck transmission.
So, with help from this forum, I've ordered REDLINE MT90.
It IS GL4 and it IS rated for synchronized transmissions.
But the reviews here and elsewhere are mixed.

Why is GL4 not widely available?
Have I missed something?

 

Call your local shops to see if they carry Redline GL-4 oil. I buy it at my local BMW repair shop.

 

$24 Red Line 50304 MT-90 75W-90 GL-4 Manual Transmission and Transaxle Lubricant (MTL)- 1 Quart

https://www.amazon.com/Red-Line-50304-Transmission-Transaxle/dp/B000CPCBEQ

You can buy direct from redline also.
https://www.redlineoil.com/find-products-for-my-vehicle

 

I have tried both Redline and this in my 5speed. Can’t really tell the difference.

CRC 24239 Multi-Purpose Gear Oil 85W90 SAE-Gallon, 128. Fluid_Ounces

$74 CRC Sta-Lube API/GL-4 Multi-Purpose Gear Oil 85W90, Sta-Lube, 1 Gallon, Hypoid Gear Oil, Yellow Metal Safe, Anti-Rust And Anti-Wear Ep Additives

https://www.amazon.com/dp/B000M8RYMC/ref=cm_sw_r_cp_api_i_lIs.Eb5FBFYZB

 

Today I rebuilt my shifter with new plastic parts.
There is some difference in smoothness.
Next week, I'm dumping out the GL5 rated MOBIL 1 and replacing it with the REDLINE MT90

 

AMSOIL severe Gear

 

One or two reasons First not selling enough to warrant keeping in stock.Why take up space for a product that just sits on the shelf

Spot Shortage of The GL4 depending where you are in the country

More and More Automatic Transmissions everyday .

Some parts of the country Transmission Shops no longer take Manual Transmission work

 

only a matter o time the white coat engineers change/revise something

or the simply dont have anything to do

as a result new entrants / many choices

Red Line has many a varied selection

good luck

 

Amsoil severe gear 75w90 is GL5
AMSOIL doesn't recommend using it in a synchronized gearbox.

 

I used to run this: https://www.pennzoil.com/en_us/prod...ls/synchromesh-manual-transmission-fluid.html
In my jeep AX15 manual trans. This is the same manual trans, the r150, that's in a 1st gen tacoma. I think it shifts better than the redline.

 

Funny because my brother put that in his generation one Tacoma AFTER it used to grind going into 2nd for at least 3 years...And it stopped grinding!
It's a super light 30w and I have no idea if it worked out long term or not because he crashed it a little more than two months later.
I hadn't considered it because I remember how thin it was.
I believe its actually GL2 or 3 rated.

 

Ok
The MT90 is in.
The shifts are notable now. As in it kind of "clicks" into each gear.
It used to just vaguely go into each gear without any feel.
The synchros seem happy.
The engagement is very different. Maybe it's a good thing.
Between rebuilding the shifter and installing the MT90, it shifts much more positively.
No slop whatsoever.
I think I like it.

 

The synchro mesh?

 

Yes

 

https://www.amsoil.com/p/manual-transmission-transaxle-gear-lube-75w-90-mtg/#pills-home_0

 

+1 on the Redline MT90, smoothed mine out a good bit.

 

That states clearly GL4.
Whatever the Hell I googled said GL5.
So, that is another actual, decent choice for a Taco transmission!

 

I am a newbie to this Tacoma World forum site. I joined to get just this type of info. My stepson has a 2014 Tacoma 4X4 with a 5sp and 4cyl w/ approx 55k miles. We're getting ready to change all the drive line fluids. Was planning to go with the Valvoline syncromesh manual transmission fluid (MTF) in the trans to meet the GL4 requirements and their Synpower full synthetic

$29 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 gear oil in the transmission and transfer case to meet the GL5 reqs. These oils are readily available at our local parts store which is one of the reasons why we're going with them. I know and respect that everyone has their personal oil preferences but does anyone see any issue running these in his 2014? Thanks in advance and glad I found this TW forum.

 

I've always used GL5 bulk standard 75w90 on my manuals. You won't have any issues at all, I've seen every oil use from cheap to special ordered Toyota MT fluid.

You will be good with those choices. Word of the wise, buy some gaskets for the drain plugs from the Toyota dealer to ensure nothing leaks after. Good luck!