I'm sure we all know that John Deere "doesn't" own a oil refinery, and has no faculty to make their own oils. John Deere may say they engineer their own oils and have a refinery to make it by their specs. Given that may be a fact, they still have someone to make the oils and chances are it may be a brand that is sold over the counter in some automobile stores or elsewhere. It turns out to be same as 10-W-30 oil
Hy-Gard oil can be used in most transmission and hydraulic
applications calling for 10W-30 or 5W-30 engine oil.
NOTE: Hy-Gard should be used in all applications calling
for JDM J20C.
–– Low-Viscosity Hy-Gard should be used in all applications
calling for JDM J20D.
–– Low-Viscosity Hy-Gard and Hy-Gard are compatible with
JDM J21A hydrostatic fluid and can be added to systems that
contain hydrostatic fluid.