10 year old motor oil has undoubtedly lost some of its better qualities regarding clinging film and anti-rust/anti foam additives from the OEM additive pack.
You can certainly justify a drain & fill.
Don't forget to fish the drain pan with a magnet (if the drain plug has no magnet of its own) to see if something has shed or moulted inside the case.
Dino or synthetic? In the case of a manual transmission, dino would certainly be OK. The option to use synthetic is pretty much a moot point here, based largely on how well you can stand to part with a few more dead presidents pictures.
Dino will do just fine.............synthetic will not harm anything inside. Your call!

I would change the oil,especially since it is a manual transmission. On whether to use synthetic or the OEM grade oil, I'd go with the OEM. It went 10 years with out any problems. What I,m not sure of is if the oil seals are compatable with synthetic based oils due to the age. Wear wise synthetic is alot better. I work on heavy trucks and alot now use synthetic lubes in the transmissions and axles due to very good protection against wear and lubricant break down which allows for extended change intervals. The warranties are also extended with these synthetic lubes.

Went well, used dyno oil. EXCEPT the trans needs about 6 quarts. Didn't think it would hold that much. So, tractors on wooden blocks waiting for me to get another 4 quarts of oil...:-) Don't know exactly how much came out, just drained it into a flat drain pan, filled one gallon jug and there's still quite a bit in the pan.

Should be good for another 10 years now.

Ev

How did the oil look? Any debris?

Tom, no debris, inserted a little cylindrical magnet to see if I could pick up anything, nope, ditto on the drain plug. Can't believe there wasn't some shavings, filings and such, guess the weight and head pressure of the oil flushed it out.

There was a little white foam floating on top of the used oil, guess that was from condensation? The tractor has never been wet or rained on, except when it and I were at a far corner of the estate and a shower popped up and I had to make a run to the barn....:-)

Thanks for the responses.

Ev

I had to ask as these are really tough transaxles. My guess is you and mownie were right- time to freshen the oil and get the condensation out as a bonus. Did you extend the life, who knows but you did what you did to treat it right. Thanks for sharing.