Older L775 New Holland Skidsteer - another "what fluid can I use" question

[befiendly]

I recently acquired an older l775 I want to flush out the systems. Specs call for 90 wt in the gearcase and chaincase and Only Dextron II ATF in the hydraulic reservoir. It has been sitting and I would like to run it with "cheaper" oil/fluid for a week/month or 2, then change fluid again. I am wondering if I can use "universal tractor fluid" or equivalent ($40/ 5 gallon) in the hydraulic system instead of ATF? The bobcat dealer also says if I want to rent their auger attachment, I have to use hydraulic fluid not atf. Would it be detrimental to run the "tractor fluid" long term?

ALSO: How about the same tractor fluid in the chaincases? any possible damage to seals etc?

Advice much appreciated. Thank you!