Rebuilding? Kits? I have fixed hundreds of these carbs and never rebuilt a one of them. Most of my procedures were similar but all started with a good test drive and enough external testing to expect a specific problem and go for it.
The biggest problem the carb had was lean hesitations and the secondary air valve stumble. The needle and seat (pressed in) will come out of the base shutting down fuel also.
MB had a bunch of modifications to try and make the later emmision cars work...none of them were very successful.
Almost all the running problems can be delt with through only the removal of the carb top. Needle and seat can be verified, float level adjusted (the height of the top of the gas should be 5mm from the top). Main jet, and idle jets and air correction holes all can be cleaned. The full activity of the secondary air valve can be repaired; the shaft passes through the top in three spots and the top is usually warped causing the shaft to bind. A little attention to the shaft and holes can clean this up if the top isn't too badly warped (watch those 8mm nuts on reassemble). The main jets should be verified at 100 taking them to 105 solves everything but fuel mileage and emmisions, many of the jets were undersized - they have probably been fixed somewhere along the line.
Now that the cars are over twenty-five years old a number of failures cause new problems: all the vacuum diaphrams (choke pull-off, secondary air valve, and idle stabilization)are failing or have failed. Accelerator pump diaphrams leak/don't pump fuel. The plastic cam controlling secondary metering rods wears out or brakes - it is unavailable.
All the parts except the plastic cam are available from MB individually.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician