How cold is cold? If cold is 40 degrees, it probably would need to have the glow plugs working or have the engine heater plugged in for an hour for it to start right up. On the other hand if cold is 60 degrees, and it doesn"t start up after half a dozen turns of the crankshaft, you might have problems. And hopefully ether has not been used, at least very often.
I do not have experience with the row crop tractors, but really like my 641Diesel. It uses about half as much fuel as a similar gas tractor to do a given job. Even though it has way more than 10k hours on it, it still starts and works well.
As far as parts availability goes, most everything is offered by someone. There is a problem with rebuild kits for the 144 inch diesel--I have not been able to find any, anywhere on the internet. But kits for the 172 diesel are almost everywhere. And possibly there could be problems with getting specific parts to the row crop modifications. But in general, the hundred series tractors are fairly simple, and easy to keep running.
If in fact the tractor is a 961, it should have live PTO, which is a real advantage for certain jobs, like running a baler. The possible downside of having the live PTO is that it uses a double disc, 2 stage clutch, which is expensive to replace if that is necessary. The live PTO 5 speed transmission is possibly not as strong as the regular 5 speed, since the PTO power runs through a hollow transmission input and mainshaft.
Unless the overall tractor is really beat and the tires are poor, I think $1900 sounds like a pretty good price. Where is it? If you don"t decide to get it, maybe someone else would be interested. Good luck!