Many thanks for the excellent description (with great photos), provided by zhandax. I can now proceed with repairs to my Bosch wiper transmission.

One clarification: Regarding the "rectangular opening with a release" . . . often described in postings: there is no such thing on my 1991 Merc. 300CE (124). Instead, there is a (1) single machine screw at the bottom of the underside of my (1991 car) clam-shell cover but that alone will not open the cover. The entire unit must be removed from the car to open the cover for repair to the gear mechanism.

If one must replace the wiper transmission, the Bosch company made (2) two units. My 1991, fits in the 1986 - 1993 period. The price found on the www for new (not used or rebuilt) is $535. Less than half of the dealer's price.

Post script: After removing the center nut and circlip, the gear shaft needed only a few stikes of a rubber hammer to drop away. Finally, the clam shell cover was opened to reveal the problem. The larger, semi-circle plastic gear, attached to the bottom half of the cover had lost almost all its teeth. The remains of what may have been grease, appeared to have dried to the point of near hardness and the gear teeth appeared to have become brittle to the breaking point.

Not Bosch, nor Mercedes offer a repair kit. Otherwise, it would have been simple and inexpensive to replace the gear surface (if) such a part or repair kit were available. Instead, the local Merc dealer's department of amusingly priced parts offered a new Bosch (model 124) wiper transmission, without the motor, for $1,300.

This is an example of why I restored my 1981 Volvo 260 GLE and enjoy driving it so much more than the Merc. That model Volvo is built with far greater engineering design, better lasting quality and ease of repair. Unlike the Merc's dreaded CD of a Service Manual Library, the Vovlo shop manual is written clearly, in logically sequential order and understandable terms.

You can amuse the local Merc dealer or go to the www if yours is also in an unrepairable condition.

There is an opening at the base of the unit's cover. With a needle grease applicator, you can squirt some lubrication to the gears, maybe once a year, depending upon use. Also, the replacement wiper tranny has an improvement: snap-off clam-shell cover for grease application.