71 280 SE 4.5 Engine Problems - Saga Continues

Here is a clear explanation (I hope) of has transpired in the last several weeks: For a couple of weeks, when I cold start the engine, I would hear a rattling noise from inside the car and it appeared to be coming from the engine compartment, left hand side. The noise could only be heard while the car is moving and it would last for about 3 or 4 minutes. Dummy me, I did not do anything about it until one day, after driving the car 15 or so miles, the car stated jerking and hesitating and misfiring so bad to the point it did not want to go past 20 or 30 MPH. It was so bad I did not think I would make it home.
Here is what was done to it: Distributor cap was found cracked and was changed. New trigger points, points, condenser, plugs, fuel filter, and repaired/checked injection wiring.
Result: When got the car back, the engine did not sound the same and was a little jerky in idle. The car did not have the power I am use to before the problem started. It is very reluctant and hesitates. It feels like something is holding it back. The car would make it to 60-70 MPH but with a lot of effort and hesitation.
Took it back to the shop, mechanic made some adjustments to fuel mixture but did not help the situation at all. The car just would not sound or drive the same. Mechanic did not know what else to do without spending a lot of money replacing bunch of stuff and recommended taking it to the local Mercedes dealership for diagnosis. I have done so today but very reluctantly. One more thing, rattling noise is not there anymore, but I have a hunch it was the cause of this whole mess I am in now.
Again, any advice and possibilities of what it going on is much appreciated.
I hope I have said enough and my mechanic is willing to provide me with any information anyone might want to resolve this problem.
Thank you again.

The noise is a mystery to me, and I have no guess as to what it may have been? First the thing that concerns me is the engine running poorly at idle. This could be caused by anything from improper dwell or timing, improper firing order, or even a cracked spark plug, providing the tech did not touch anything but the components you listed. Second the fuel filter may have been installed backwards. This in itself can cause major problems "voice of experience ". (NOTE: I AM NOT familiar with this vehicle as to if it is injected/carburetor. I am using basic "Sure-Luck Holmes" deductive reasoning in a logical approach to diagnoises.All vehicles run on physics! ) The Mercedes dealer will tell you what is really wrong! And if it is something you feel you can do your self pay them for their time and fix it your self! With all the Wannabees like Me! and parts from Fastlane, what more can you ask for! Good luck and let us know what is is/was!

You should check each cylinder for compreession. More than likely one or more of the cylinders is damaged, or is not getting any compression.

Super pictures of your '61 and '65. You use that 230 as a daily driver, WOW!
I was lookin at a 1967/8 200D. Blue. He just lowered the price, but a very underpowered car cause its an automatic.

yea, the 230 is a six cylinder, and has just enough power, and has a manual transmission (on the floor). If it weren't standard, it'd be a different story. I can't imagine how much slower the diesel model is (i've only driven modern diesels, and they're wayyyy too slow), but what you lack in speed, you'll make up in fuel savings and reliability (no carbureators), which is a worthy trade-off. How much is he asking for the 200d? Blue (light blue) is an awesome colour for 110 cars. Blue and beige (like mine).