International Harvester T-340 crawler.

[dajain]

Customer brought this IH T340 crawler into my shop in pieces, I have it back together now and noticed the Hydraulics (bucket lift) uses the fluid in the transmission.
my question is, should this be filled with hydraulic fluid or gear oil?
My guess is hydraulic fluid but would love some input to be sure.
Thanks for any replies ahead of time!

 

[DJ54]

Hy-Tran, or it's equivalent
.