Mercedes 300SD Transmission problem ?

Dear Experts: Hope someone can help. Before describing the transmission problem. MY 1984 300SD has leaks from an injector. It is the hard line plus the hose. Don't know if that leak affects the tranmission problem I have. Also, since April 2006, when I bought this 300SD, there is a loud clunk sound, when I go into Reverse. After doing 70 mph for 20 minutes, at a stop sign, problem started when I need to reverse. There is a horrible sound when I go into neutral, reverse or park. Within 5 seconds, it did go into reverse, and no problem in D, 2, or 3. At a parking spot in a public parking lot, The horrible sound repeated when going into N, R, or Park. I turned off the engine. When I turned the key, without effort of turning the key all the way to crank, the car started, and I have to move the key myself to bring it into the non cranking position, or I would burn the starter. An hour later, I come back from grocery shopping, the same cranking problem occurs. The car has the horrible sound in P, N or Reverse, and it was able to go into reverse after 5 seconds. But it refuse to get out of first gear, I think, after in D. I pushed the accelerator to the floor, in the parking lot, and the car moved slower than an old lady walking with a cane. I went from D to 3 and 2, and the car died. For unknown reasons, the car started acting normal from this point. Cranking, Starting, Reverse, Neutral, and Drive. What happened ? Can someone tell me ?