Keep an eye on the engine temp gauge. In windy conditions trash can build up on the radiator. If you see temp rising, just open the radiator door and scrape the trash off with your fingers. I always blew my radiator out every night, but in barley, trash could build up 3 times a day if it was windy.
There is a warning buzzer, but it's got to be better if you can pick it up before it gets that hot.
This goes against the manual, but I was told to aim to get a clean sample with the pre-cleaner fully closed (in cereals), and then gradually open it up until the sample got a little dirty, then close it a fraction. This gets a bit of extra capacity out of the sieves, but mostly your capacity is limited by the walkers.
While on walkers, there are several threads about it if you want to do a search, but to keep it short, use plenty of grease if they are the greasable type, or switch to wooden blocks which will be more reliable and hassle free.
They're a good honest machine. I think I only had three bearings fail in 4000 hours on ours. With correct lubrication, it's mainly belts, chains and sprockets to keep an eye on.