Yes, you can use 75w-90 gear oil instead of SAE 90 gear oil
Manual transmission will take 2 1/4 quarts of 75w90 api gl-4
Manual trans. API GL-4 SAE75W90W or 80W90W gear oil Differential API GL-5 SAE 80W90W hypoid gear oil Transfer case API GL-4 or GL-5 SAE80W or 90W gear oil
SAE 80 API "GL-4" hypoid gear oil says Yamaha. Replace every 16,000 miles or every 2 years. I use a synthetic 75W90 which meets GL-4 and GL-5 requirements. Fill to the top of fill opening.... About 198cc- from memory.
1986 to 1996 Manual Transmission and Transfer case use API GL4 or GL4 and GL5 80W90 or 75W90. Differentials use API GL-5 SAE 75W-90 or 80W-90 lubricant. Do not put a GL5 gear oil in the transmission unless it says GL4 and GL5. GL5 will attack the syncros.
You can use API GL-4, SAE 75W90 semi synthetic for your Galant. There are standard types of oil used in these types of cars.
sae 40, api cf
The recommended fluid for the b2500 is API GL-5. Alternatively, SAE 75W90 or 80W90 transmission oil is used in many places.
The 1999 Hyundai Accent GL recommended transmission oil is API GL 5, SAE 75W90 semi synthetic transmission fluid. The transmission fluid can be purchased at any auto parts store.
Remove fill plug on transmission, followed by the drain plug. After the fluid has completely drained, reinstall the drain plug and fill with 2.25 quarts of 75w85 manual transmission fluid (or 75w90) USE API GL-4
Gear Oil API GL-4 or GL-5. 75W-90
API GL-4 SAE 75w90w or 80w90w. That is according to the Haynes manual
4 pints (1.9 liters) SAE 85W-90 gear lubricant API grade GL-5.