... and finally
Don't forget the heaters. Last year I collected a tractor that had its rear window broken with some 'loaded' snowballs when it was parked in town. I drove it through the snow to the garage to fit a replacement window.
This was a relatively modern tractor with low hours and, with the exception of the broken rear window, was in excellent condition. But I could not get the heaters to blow any air, hot or cold, even though I could hear the fan running. And without the rear window, it was bloody cold. Halfway into the 50-minute journey, I decided to investigate. Under the bonnet is where the heater unit and its filter were housed on this particular tractor. What I found still makes me laugh; someone had fitted the heater unit air filter while it was still in its bag, presumably to keep it in good condition. Removing it from its plastic cocoon allowed air to flow through it and into the cab. It had been like this for some time, perhaps a reflection of how mild our winters usually are.
... And finally, finally ... Similar to the motor trade, many agricultural machinery dealers are offering winter checks and servicing, so it's maybe worth a phone call to your local dealer to see what is on offer.