I have repaired these before and usually had to look all over the shop floor for little balls and springs, well not this time.
The switch is not broken, only dried out lubrication.
So I revitalized the switch lube with a quick shot of WD40 under the rocker. Waited a few minutes then work the switch back and forth till smooth and like new. Time to do all four, about 10 minutes.
Another The Easy Fix from the gears.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom