Redline MT90, Amsoil MTG, Ford XT-4-QGL and XT-M5-QS ... are your 75w90 GL4 manual gear oils. You can also check with your local Toyota dealer but make sure you see the PN. Most dealers will just use GL5 bulk gear oil and call it a day.
And the GL5 corrosion issue is definitely over-hyped. Your 30k interval should be fine with just about any gear oil. To have a corrosion issue, you'll usually need to run the gear oil too long(buffering additives used up), add water to the transmission, overheat the gear oil, or a combination of the 3. The issue with most GL5's is that they come with a variable dose of LSD additive. Some manuals don't respond to LSD additive and make shifting difficult. Other manuals shift smoother with the additive. Trial and error!
The GL5 gear oils, like Neo 75w90HD, RoyalPurple Maxgear, Motul Gear300, Redline 75w90NS, Ford XT-75W90-QGT, Eneos MT, Silkolene Silktran Syn 5, Synlube, Idemitsu MTF, Torco RTF ... are some that deliver excellent results.
Toyota has moved to an LV-MTF on newer manuals. Nissan, Kia, Hyundai, Mitsubishi, GM, Chrysler also have moved some gearboxes to a 75w85 gear oil, instead of the 75w90 or 80w90's that were used for years. If your climate is colder, I see no reason to use the 75w90. The various OE PN's in 75w85 are easy choices too and what I would use. The 75w85 is what happens when you mix Redline MTL with MT90, or Amsoil MTF with MTG. This mixing of like fluids/brand is a common way to thin out a thicker gear oil to improve shift quality if residing in the northern states, or if you have a grumpy transmission.
