2007 ML350

My wipers have been acting goofy- they will work on startup for a few minutes then nothing. Sometimes not even on startup, just no response.

The rear wiper functions fine, the wiper spray works fine, I've checked the relay and the fuse, they are both in working order.

I drive a lot for work in a rainy area so I need my wipers- does anyone have any tips on how to approach this issue?

Thanks!