My car is an '87 300D Euro 4matic sedan. Problem is combination turn signal lever won't go back to center neutral after making a turn.

The MB dealer replaced a small platic ring (cheap), but charged a lot for labor. Lever was okay, but after a week, I'm have the same problem again.

Is the plastic ring easily replaced by a DIY? What could be causing this recurring failure? Force needed to manually flip the turn lever is normal.