Sorry 85Hokie, and ruger1980
This is definitely a case of, don't guess, read the manual!
It's not 80-90 gear Oil, WAY TOO THICK
It's NOT UDT or SUDT not enough of the right lubricants in it.
It is SAE 80w gear oil and SAE 80W is not the same as 80W 90
80W gear oil is really hard to find, and when you do it's real expensive.
80W gear oil is the same as 30W motor oil and they are interchangeable.
Again not 5w30 or 10w30 or any other mix it's not the same.
There is a lot of documentation on this because older Bobcats called for 80w gear oil or 30w in the hydraulic systems, and regular hydraulic fluid makes the drive motors chatter.