It means that your lock cylinder in the driver's door is starting to go. It has a U-shaped connector that is at the end of the lock cylinder assembly which is inserted into the door. The U shaped end allows a slight swivel when turning the key. The end of the U shaped piece inserts into the actual door lock mechanism and does the physical locking and unlocking, including operating the vacuum lock/unlock system.
As a side note, the lock cylinder also has a three wire connector that enables/disables the alarm system.
When one side of the U breaks often while the other side continues to stay connected you get this "slowed respones" to the turning of the key. What happens is the twisting (torque really) from the key use makes the U part fail.
The bad news is about $350 for a new lock cylinder with a key cut to your chassis #. Additional bad news is that the broken U-shaped piece is not avaiable separately and the claim that it cannot be repaired.
Across several weekends I have explored and researched the above with regard to the 190e which, BTW had the same symptoms and problems.
The good news is I repaired the lock cylinder U-shaped connector.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)