If you are looking at coupe or cabriolet seats , the presence of a vacuum line is for the backrest locking mechanism which operates by vacuum only when the doors are closed AND the engine is running .
I rebuilt a pair of ortho seats found in a 190E donor car , I had only been looking for a replacement seat base for my 190 2.6 but decided to incorporate these as I found them .
I did previously post the full sequence of pictures showing how to remove , dismantle and rebuild the seats , however , for this thread I'll only post a few showing the ortho bits .
This was my drivers seat with broken springs in the base
The springs were OK in the donor car seats , but the covers were a mess : I used the spring base and fitted the cover from my own seat back onto it .
The donor backrest shows the condition of the covers , had the seats not been orthopaedic I would just have thrown this away
Here is the small control unit on the side of the seat
Looking inside the backrest there are air pipes to each bladder from the control unit
These can be unplugged for removal of the cover