Toyota, Mazda, and various automakers state GL4
or GL5. None state whether to avoid LS additives or not. None mention whether you need a certain chemistry or not. When it is a blanket broad automaker recommendation, I would purposely AVOID LS and GL5 gear oils when GL4's are available and an option. As long as Redline/Amsoil are around, use the GL4!
Would I use the XDM? only if no other GL4 was readily available. Availability of a GL5 non-LS Mack GOJ+ 75w90 is everywhere and have yet to see them NOT work in a manual transmission from Toyota, Mazda, Hyundai/Kia, Subaru, Nissan, Mitsubishi....
Delo Syn-Gear XDM meet and exceed the requirements of API Service Categories GL-4, GL-5 and MT-1.
Is it the best choice? That is for the owner to decide. But, XDM does fall under the non-LS GL-5's and CAN be used whether I recommend or not when the automaker states a GL5 can be used.
We've used GL5's and GL4 marine gear oils in the shop since the 1980's and NEVER had one come back with synchro problems. Suddenly, every manual owner is either too incompetent to drive a manual, or too lazy to change the gear oil out regularly, has problems with so-called chemistry, synchros, or certain fluids. I'd also guess that maybe the LS additives weren't standard ages ago like now. Or, maybe owners weren't limpwristed snowflakes back then and were man enough shift a transmission with straight 140 grade when its 0°F outside.
Enjoy the OTR EP fluid in your transmission because your automaker allows a GL5 in the owners manual.
BTW, no need to turn this thread into a classroom. Nobody cares about the chemistry of the fluids or how to blend them. Save it for your students. And, yes, some of us know but don't brag about it constantly. The debate and requirements of a spec is irrelevant. Oh, and yes, I under what is required for the GL4/GL5/MT1 specs. Big fooking deal. Do you know how to make a syncro or a transmission gear? have you ever made one? or how to tear a manual transmission apart, address shortcomings on prototypes, and put them back together updated for said shortcomings? Yes, its all irrelevant to the OP's thread.
And again, do not use Pennzoil Synchromesh or the equivalent Valvoline MT fluids. The OP requires a 75w90 but didn't state year/make/model or owners manual requirements. The Pennzoil 75w90GL4 was still available at distributor but not sure anyone wants to buy a pail. And the Valvoline 75w90 GL4 was VIOC only, and anyone near a valvoline instant oil change quicklube can visit them to see if they still have it.... just be careful as most VIOC techs won't know the difference between the 75w90 and the GM synchromesh versions of the Valvoline MT fluids.
My only recommendation is to change the gear oil out more frequently. I don't ever use gear oil for more than 30k miles 3-4 years.
And, for the OP needing to verify a working salvaged transmission prior to using Redline...., my previous recommendations stand. Yes, the 40 to 50 grade motor oils, the GL4 90 grade marine oils, the GL5 non-LS gear oils are great to verify function, transmission sealing, and for salvage yard transmission debris cleaning. The only way to install a recycled gearbox, imo, is to rinse it once, prior to sending it back to the customer. Nothing worse than their fancy Amsoil/Redline fluid leaking out in their driveway, or the transmission is worn out an whines or doesn't shift well enough. Someone preaching, and not wrenching, wouldn't understand this.
www.valvoline.com
