Driveshaft view and advice?
 

Here is a pic of the front driveshaft I asked my mechanic to send me to determine if this was original or a replaced shaft.
I am NOT mechanically inclined, Im a Physician with no time to be spending under the hood even though I wish I could. He tells me there is a single grease fitting but from my view this appears to be a double cardon shaft, or am I mistaken? Any input appreciated but he says the shaft looks great for having 120,000 mi on the vehicle. It is being serviced for the 100k major service outlined on this forum and I specifically had him check the shafts as well and grease them if they were greasible.

It is a double cardon shaft... but, if there is only 1 grease zerk, then it needs to be rebuilt/replaced to have 2 grease zerks. One on each u-joint. I had one of mine rebuilt for about $180 and it is pretty easy to take out and put back in... only 4 nuts & bolts on each end. Once I get things settled down, I'm going to have my other second D2 shaft rebuilt.

What I'd be worried about, the drive shaft may look fine, but it's the insides of u-joints that are going to give you the problems. You have an original shaft and it should be updated... to answer your main question.

it has had at least one u-joint replaced at the differential you can see the zerk fitting sticking out the end.
It is hard to tell about the double cardon, there are not fitting on this side, that does not mean they aren't on the other side and not in the photo.

Thank you Matt, in fact I have already purchased a new shaft from BP Utah, $365 shipped, double cardon with 4 grease fittings if I am not mistaken, I will let my mechanic know I will be providing that to him next week, and hopefully with that installation and the full service being done on it I will be ready to tackle the Northeast winter getting me to and from work reliably. I appreciate the input.

Are you sure thats a land rover? It looks very dry under there.
My only advice is to triple check the rebuild price before he moves forward. An average rebuild is not a big deal for a mechanic but the D2 takes longer and parts can be more with the zerks. He might quote you $200 but then it'll end up being $450. You can find a new or rebuilt shaft with zerks on-line for around $300. you wouldn't want to pay more for a rebuild shaft.
my 2 cents.

I purchased a shaft form BP Utah, a new one apparently, not a rebuilt shaft, they have double cardon shafts on ebay but I called direct so as to get more info on the shafts, built in the USA , here's the link:
Land Rover Discovery 2 II Heavy Duty Front Driveshaft Drive Shaft Propeller TVB000110 TVB000320

and I have dealt with these guys before and they seem to run a very good operation. I guess I would rather put a new shaft on there rather than have someone rebuild it, especially if they were not familiar or experienced as such, much like I wouldn't want an orthopedist removing my appendix sort of a thing....

Is the centering ball greasable on their shafts?

yes .... 2" diameter & 120 Wall DOM Shaft
DANA "Spicer" 1310 Center Greasible BLUE U Joint
Long Travel Slip/Spline
Polished/Black Paint Shaft
Strong Weld
Dual Balancing (High/Low Speed)
Offroad Proven Performance

.....and I might add new brakes, thermostat, bleed and flush, psf, transmission service, throttle body and intake servcie, differential fluid flush, change, transfer case service, new spark plug wires and plugs ngk, air filter, new serpentine belt , front driveshaft installed(my purchase) and all fluids changed to spec per the major service... $1900 later...and 2 more weeks in the shop, but I'd rather be safe than sorry and if he needs it done, then damnit, he's gettin it done!!!

Yes, five grease fittings and not four.

See photo below to find the 5th fitting.