This is my first contribution to the forum since getting the SL a couple of months ago. Have multiple issues to deal with but one was the door lock problem. The penny fix inspired me to have a go at my own solution that I am sharing.
original penny fix.
MB 300SL
What I did was go buy a CPVC 1/2" pipe cap from Home Depot and cut it down, press it on to the original broken plastic lock component and use a small screw to operate the lock linkage. i did have to slightly bend the linkage to get the clearance I needed. I did file the lettering off the end of the cap and if prepared properly I think bending the linkage would be even more minimal. It is a tight fit, i had to use a vice to press it on. Of course you need to be careful to not to muck up the linkage and perhaps, most importantly figure out why it broke in the first place. In my case the lock had not been lubricated for some time and it was clear that the latch mechanism was sticking a bit which would cause the lock to jam. Used much white lithium grease to get everything moving smoothly.