I can only try to help with a few items.
Did the shudder and ABS light manifest about the same time? I'd be looking at the OVP again, perhaps you need a new OVP (since you changed the fuse already).
Low oil in the suspension resevoir. Get some MB suspension fluid ASAP, hopefully you didn't burn the pump. Yes you can open the top and run the engine, the return flow of fluid is a slow steady trickle, no worry about splashout. When you fill the res, fill it to just above, like 1/4", the top rib of the bottle.
If you've lost all the R-12 from the bad hose, yes you can DIY then have it charged with R-12 at the shop.
Rear seats not moving, are you trying with the door open or closed? I found that the seats don't operate on mine with the door open.
Is your "ghadak" coming from the front end when you go over bumps/potholes? Most like track rod mounts (part of the front suspension).
Last question. Is you mechanic a MB specialist or Independant, or the dealer OR is he a mechanic not familiar with Mercedes?
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.