You won't go far wrong in using what the manual calls for.
I have not had an ES or manual for one but 20 or 30wt standard motor oil works well. NO super antifriction additives! They keep the cone clutch from holding. BTW Irv probably has a different tranny than yours.
Irv's Overdrive is a type D and Ron's is a type J. Irv has been using gear lube since new and thats over 2,700,000 miles as of this past weekend at Ipswitch, Mass. meet when I spoke wth him. Great time if you missed it.