65 4000 diesel, all the sudden hard to start, and blowing...

Hello, looking for a little help, my 65 ford
4000 3cyl diesel just started giving me
trouble all the sudden. A little history the
tractor sets alot, only use it to and the
box blade to move gravel and snow. I do try
and start it once a month and run it for 30
min or so. The injector pump was rebuilt a
few years ago, due to faulty umbrella seals,
but not "retimed?", because the tractor has
always started pretty easy, as long as the
weather was warm. I used the it a week ago
to drag some gravel around for a couple of
hours and everything worked great, started
easy, no problems. Yesterday I go try and
move it, it doesn't want to start after a
few times of me trying, so I give it a shot
of starting fuild, it finally starts, but
looks to be running really rich, due to the
black smoke, then i notice the air breathing
housing on the hood is pushing out air and
oil, which I assume is out of the oil bath
for the breather. So I shut it back off and
trying to research my problem, but haven't
had any luck. Anyone have any ideas where I
should start, I'm really at a loss on what
to call this or what to do, thanks chad

Well I do not do much with diesels but to me it sounds like it could be one of a few things. Return line clogged up so getting extra fuel in the cylinders. Maybe a sticking valve which could cause the air cleaner type of problem. Or maybe an injector that is going bad

It sure has me stumped, the stuck valve sounds like that may be the way to go, since the breather housing air pusing out, but that just a pure guess on my part

I know just enough as for a diesel to be able to fix the simple stuff. I do a lot of work on some of my friends machines and a lot of them are diesels so I am slowly learning a good bit more. I know to first and simplest thing to check is the injector return lines which should if I remember right be sitting on the same side of the engine as the injectors do and will be right in the same area. I keep my friends Ford 4600 running so I do have at least a good educated guess as to where they are