If you are CONVINCED that the hydraulic system is properly bled, which can be a challenge sometimes, then it is time to get to the clutch.
On my first 240D, a '77 model, I had one of the diaphragm fingers break off and jam the clutch so it couldn't release. I would be shocked if the input shaft is frozen to the pilot bearing. These enginse have the best pilot bearing I've ever seen. My current 240D had the same pilot bearing for 380,000 miles. I finally replaced it at engine time.
I have in the past replaced a clutch/pressure plate/TO bearing only to find that the problem was hydraulic, so make sure before going to the trouble. A clutch job on these cars is a pain from underneath. The last time I put a clutch in my 240D I pulled the engine and it was easier. I have a walking beam in my shop so I'm better equipped to work above the car than below.
Bleeding a clutch is not as easy as brakes. The best way is to do it bottom up. Figure some way to push fluid through the bleed screw at the slave cylinder. You could fashion something from clear plastic tubing and a large hypodermic syringe or turkey baster.
Best of luck,