I fear my clutch has broken, but hopefully it is something simpler.

The car is a 1980 MB 240D, I've had it for one week.
The car had a jerky shift (it's a manual trans) when I bought it, but I had read that these old diesel MBs have "herky jerky" transmission, and the car runs like a top otherwise so I paid no mind.

Well today I went out and started it up and cannot get into any gear.
The clutch has very little resistance and I physically cannot put it into gear, although I can try to put it into R but it grinds so I don't go all the way.

I just changed the diff fluid, and what came out when I did it smelled burnt., it was nasty.
The car shifted like butter after that, while still doing the lurching when shifting into gears, mainly 1st and second.

I have had another stick shift, and have never experienced this, but maybe I've been lucky.
The car has 260k, no rust, engine sounds wonderful, interior is clean, and I don't want to lose the car.

I spent all I had on it, 1800 bucks, and don't have much to spend to get it fixed.
I have changed the oil, fuel filters, air filter, diff fluid, and did a valve adjustment (which made a huge difference, remember to adjust your valves, I cannot stress that enough!).

I can get a new tranny on ebay for 300, or get a clutch kit for 200, but don't know if I need to, I have checked the shift linkage at the transmission, and there is nothing out of place that I can see or feel.
There is no fluid under the floor mat, and no leaks under the car.
I need your expert opinion, I may have it towed to my local MB guy, but would like some more info before I do, to save his time (and my cost.) I would love to do the work myself if at all poss.

Thanks in advance for your words of wisdom.