Door Knob Blues
 

I Have A 1990 Benz 4dr Sedan 300e With A 3,0 Engine.
For Some Reason The Door Knob On The Left Front Door
Will Not Press Down, The Other Doors Will Lock When
I Press The Right Front Door Knob. Please Advise.
Pgivenss

Does this happen with the door closed?

I think it is standard operating procedure NOT to be able to push down the drivers door lock when the door is open..

this is to prevent an unintended lockout.... it was that way on my 1972 280se...

i have never checked my other cars.

That is meant to be the case... so you don't lock your keys in the car from the door that you got out of the most.

Now, if it doesnt lock when its closed from the inside... then you've got another issue.. not sure what it would be... never ran into it.

lock trouble
 

I had the same problem, it turned out to be an actuator that wasn't working...
good luck