Diesel tractor smokes blue smoke excessively?

Have you tried a compression test to make sure the rings haven't worn down or lined up to leak oil passed them?

Does that have a oil cooler type part that mounts on the intake of the engine? That could be leaking oil into the intake.

So how do you know blue smoke is oil? because in my 20 years experience if your burning that much oil to be smoking like that the old girl ain't gonna run, and I'd say by its vintage its not turbo charged, if so you could suspect a bad seal there, but generally an injector is my first suspect, although I cant smell the beast from the video, nice touch by the way, but the Cav Lucas and Bosch type injection systems IH used where pretty known for failure, but before you start throwing money at this thing remove the injectors and bring them to a good diesel shop and have them tested, only takes a minute and there easy to remove in most cases, however some of the old Cav's can grow roots and be a real pain in the butt to remove, in which case I'd suggest lots of penetrating oil, so lets hope you have the Bosch type, if these check out to be good, which I doubt they will, I got some bad news for you sunshine, you have an injection pump problem, its either jumped time or you have a metering spool stuck open. Bummer.

It could be a worn seal. As mentioned before it could be injectors. It could be broken piston rings even if they have been replaced 2 years ago. One problem I had with an MF165 was the seal between the fuel lift pump and the sump went to it was sucking oil in to the fuel system. This could be the case. Also it could be the heater plugs are not working.

I'd start by removing the injectors,2 reasons,I'm not convinced by that smoke colour,a test by your local diesel specialist will rule them out or in,

and while they're out do a compression test and a compression leakage test if possible,much more accurate and it gives more useful information.

And I'd also check the piston heights at top dead centre through the injector holes,they should be all the same.

If these 3 things check out then it's pump off time and off to the re-conditioners

As mentioned, you need to determine if the engine is consuming oil abnormally. If it is not using oil, you may have faulty fuel injectors that are allowing too much fuel to be burned. You should probably have the fuel injection system diagnosed/serviced by a qualified technician/shop. Obviously if the engine is using too much oil the only recourse may be to tear it down again for further diagnosis.

I would try injectors first. It's the one thing you haven't mentioned as worked on. Sounds like they need recalibrating or new tips.

Do you have an air cleaner with oil in it, some do, then it could be that with too much in it.

how much oil is it using?