20W Oil for Eaton 7

[shallowwatersailor 3,213]

I like to do a full service on my new tractors. Is there a substitute to use for 20W oil in the Eaton 7 transmission? Is it detergent or non-detergent? Amsoil sells a 10W non-detergent but I think that might be too thin and 30W non-detergent too thick. I am having trouble finding straight-weight 20W. The WH manual actually says that the transmission is not serviceable. I know the transaxle can be serviced and uses 10W-30.