Does anybody know if the internal plastic gears, which cause the pump action on the mono wiper available to buy separately from the whole unit please?

The bad news: The gear parts are not available. You have to buy the entire assembly. Last time I check it was around $950.

The good news: If you can get a wiper assembly from an early 190 E the gears are the same and they are made of bronze. They are a direct replacement for the plastic gears and they last a great deal longer.

You could pick up an assembly such as this at a wrecking yard or on E-bay. I might even have one around here I could sell you cheap. I would have to find it first, so you would likely get quicker results just buying one used somewhere. Most used ones go for about $100.

You also need to get some good grease to put on the gears when you replace them. I used Mobil 1 synthetic and it worked great.

Idcelr8