What Hydraulic fluid to use in an older L775

Hello, new here. I have gotten a headache trying to find out what to use. Everytime I try to search I get threads on tractors so let me explain. I have a 1980 L775. I had a "mishap" and broke both Bucket cylinders. Luckily I sourced two used ones and am ready to install and refill. We had always just dumped whatever hyd oil in the machine in the past but now realize it may need a specific fluid. The dealer said use NH 134 which is 80$ for a 5 gal pail and the dealer is 1.5 hrs away from me. I have not read spectacular things about Traveller (warren ind) from TSC but I don't have wet clutchs in this . The Delaer said any decent Hydraulic/trans tractor fluid should work fine...Was thinking about rotella HD tractor fluid ? Thoughts ? opinions ?

If it's ydrostatic drive, you need thicker oil to prevent pump damage.
I run engine oil in my machines, 20W50 but it really depends on the climate you live in. If it gets really cold, 20W50 is too thick in winter.