Need an oil for my gearbox.
 

My 1994 Geo prizm (Toyota corolla) has a 5 speed manual. It shifts like garbage when cold, I am running this (75W-90 GL5 Valvoline.com > Products > Grease Gear Oil > Gear Oil > SynPower® Full Synthetic Gear Oil )in it. By garbage, I mean that it is almost impossible to avoid crunching in the lower gears when it is cold.
What gear oil should I use?

Pennzoil syncromesh is one that a lot of people use in manuals. I'd do a little research before you make a decision. Could also be possible that your syncros are shot, but hopefully a better fluid will clear things up for you.

Do not use a GL5 oil... Go out and buy some Redline MTL or MT-90 GL4 manual transmission fluid. You will notice the difference immediately.

I once swapped in a GL5 oil in my old '09 Vibe. It was instantly hard to shift and after the first day, became impossible the shift into 3rd without double clutching. Different transmission, yatta yatta... but the premise is the same, you can read up on the poor performance of gl5 fluids in small cars on many forums.

Red Line Synthetic Oil - Gear Oil for Manual Transmissions - MTL 70W80 GL-4 Gear Oil

You can find this product stocked on the shelf at most hotrodder/aftermarket performance shops. Napa ect won't stock it.

Do you have an owner's manual? If so, it should tell you what kind of oil to use in the gearbox. Some newer manual transmissions actually use ATF, so a regular gear oil would be far too thick for them.

-soD

The manual for the geo prizm says that I should use SAE 75w-90 GL-4 (GM part number 12346074 Castrol Syntorq GL-4 or equivalent) or SAE 75W-90 GL-5 gear lubricant.

I love the Redline MTL.

+1 for Redline MTL. Helped my car shift better in cold conditions.

If I have to buy a gear oil at a B&M, what would be recommended?

Buy Redline MTL or MT-90 GL4. Nothing else. Any GL5 product you put in your transmission will do the exact same thing it's doing now so don't cheap out. Find a store that sells Redline or buy it online and have it shipped.

No compromise!

If the syncros are brass your sycros are quickly being destroyed by the GL5 oil.

Here is an article that helps explain why you should not use a GL5 oil in a sycromesh transmission.
http://www.widman.biz/uploads/Transaxle_oil.pdf