You wanna look at the whole thing when you buy a second hand draper. Steer clear of them if they arent perfectly straight. You will see it if you get it lifted up from the ground with a combine or something. Dont conclude that it is straight if it sitting on the ground.
Then you wanna look at axel that runs along the left hand side of the header. It transfers power from the gearbox that has a pto shaft which connects to the feederhouse. Where the axel from the left hand side connects to the gearbox you gotta inspect it very carefully for any cracks in the metal as those thing will just break on you without any kind of warning.
Spin the reel! spin it about 30 degrees every time you grab it, and if it suddenly takes off and spins more than that, it means you got a bend in it. And those are just pricks of things to get straight again.
Sit in the middle draper that feeds into the feederhouse, and push the draper rollers with your feet as hard as you can. If you cannot move them in, it means that the draper belts have been shortended all they can, and if you get a tear in the draperbelt later on you cant fix it without getting a new draperbelt.
Check the bearings on the wheels on each side.
Have a good look at the wobblebox. There should not be any to very little play in it when you turn the pulley on it. If there is any,it will cause you trouble later on. trust me. even if greased proberbly.
Look at where the the spring packs is joined onto the actual platform, and the carrier. The curved section that wraps around the pin can break and you wouldnt even know about it before you have parked you combine on top of it.
And finally, if you can get a combine hooked on to it while youre looking at it, check for leaks at all the hydraulic motors that pull the drapers.
ahem... Other than that, they are really good headers, and they will cut really low, if you pitch the whole thing forward.