THERE is NO CHOKE on a deisel. I guess you missed that when D Piolet said that. You should not have to use anything to start your tractor esp on that new. Myabe if it was like minus 20F or something it may be acceptable if you HAD to get it started.
I still think you have a problem. My 30+ yr old yanmar with an unkown history will start after say the second attempt with no glow plugs or the thermostart system on it down to freezing temps.
As to the WD40 thing i read on here that that was true of the old formula but the new one was changed due to "huffers" and it is not as good to use as a deisel starting agent.
Moving right along, she will start with no starting agent! Tractor has more power now and never bogs down. The man that owned it before me just about screed it up. Never changed the oil or fuel filter ext. Took care of all that. Thanks and have a nice day!