Many thanks for the kind comments, Brian. I agree on the final drive oil specs. We have been running 90w gear oil in the final drives on all our AC's for about 50 years now. In all that time we lost one final drive bearing on a CA and I'm not sure it wasn't a faulty bearing, but then again that happened on a 1951 CA in about 1985, so go figure!
If you look on the oil viscosity comparison chart on one of the links on my site (included below - the chart is some way down the page) it shows not much difference between 80w gear oil and 20w engine oil. Different designations, different applications, but similar viscosities. I thought that was really interesting. Mine all have 90w in the final drives and that's what I'll stay with I think - it works here in SC. *But* that's not in the manuals or the new recommendations from AGCO and as you guessed I'm posting official recommendations and not what works for me, since it may *not* work in another climate!