Only one plastic ring gear about 3" diameter. The other is a metal worm gear.

However, I'd take it apart first. Sometimes it's the motor. I bought motor [with integral transmission] assembly for $75 from junk yard through "car-part.com" and saved on shipping by not getting the entire arm assembly. A failing motor will swing the arm, but not as fast as it should.

I'll assume a 190 is similar to my 124 in that:
1] it takes more time to remove all the plastic surrounding the cowl, than to pull and dissemble the wiper motor trans assembly,
2] the heater motor is under the wiper assembly and its the ideal time to pull the heater motor and lubricate the squirrel cage,
3] change cabin air filter.