Good to know. I would probably make a right hash of the painting job, and it would end up looking worse I think! Such a small thing, and yet so annyoing...
It's pretty good using an aerosol.
You'll need to screw the glove box and release the button, lock and latching mechanism from the car. Take the part to Halford and ask them to match and mix the colour and put it into an aerosol can. You can get as much as you want because you can use the aerosol on other area of the interior of the car.
Test the aerosol on a white cardboard or papers to double check the colour is matching and practice your spraying technique. In terms of painting, you should start the motion before pressing the spray button and release the spray button while your arm is still moving i.e. your arm should be moving continuously and smoothly both before, during and after you press the spray can.
You'll need to strip back all the charcoal grey area back to the transparent white surface where the light shines through - DO NOT STRIP THE CHROME STRIP ON THE BUTTON THOUGH!
Then mask the chrome strip on the button.
You can choose to prime the area with white plastic primer - I don't think Mercedes had primed the area and hence the bubbling and peeling.
Check whether you have paint on the chrome strip. If you haven't, redo the masking as before and paint 4 layers of paint on the lock surround and button.
Re-check regularly if you have paint on the chrome strip. If you do, swipe off immediately and use as little thinner as possible.
Re-assemble and job done for at least the next 3-4 years.