I run 20w50 in mine. You don't want to use GL5 in anything with synchros. The GL5 additives don't work well with brass. GL3 is available at most tractor supplies.
It actually calls for GL4 in factory manual. The brass synchros dont wear with that particular oil. Just drained the 140 out to put in 90. The 140 was hard to shift until it got warmed up.