a) First Mercedes was a used 1963 300SE with air suspension. It had crack in the main air valve diaphragm. Having no money for a new valve (dealer only, would cost more than I paid for the car) and no kit to repair (Mercedes and Bosch USA "said so") I found that it could be repaired with "crazy glue". It would hold for a few days. The process was repeated quite a few times until I found a junkyard that had a valve. After that, found that Bosch in Germany had repair kits on the shelf.
b) Driving the 1986 190D 2.5 on I95 during rush hour, lost throttle. Managed to change 2 or three lanes while coasting and got to the shoulder (alternative of being the idiot that stops in traffic didn't appeal to me). The plastic stop at the end of the throttle cable had failed. Found a can, tore it apart using the tool kit pliers (have never used them since). Bent a piece around the cable and was good to go. Bought two new parts, one to use and one as a spare. I think the spare is still in the glove box 15 years later.