Can I buy a replacement for just the gear?

Motor works fine, and ps to ds sweep works every time. It sticks on the return sweep every time.

The black plastic that covers the shaft on the inside of the window is loose.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT