I had a similar issue with mine breaking the return on one direction, but once I took it apart I found that it wasn't repairable, but rather replaceable.

The turn signal switch assembly just has a plastic toggle that catches the steering shaft to reset the signal. Once it's broken, it's easier to just replace it.

When I replaced mine, it took removing the three screws that hold the knee bolster to get to the two connectors on the bottom, one bolt that holds the steering wheel onto the steering column, and three screws that hold the turn signal assembly in place on the column.
You then get to pull the assembly up out of the steering column shell and guide the wiring harness connectors up the shell as well.

Installing the new, or usable used switch is just a matter of reversing the same order of steps.

Easily fixable with a phillips screwdriver and a 10 or 12 point hex key socket to remove the steering wheel securing bolt.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...