'92 300SE

Recently while sitting at a stoplight, my windshield wipers just stopped wiping in mid arc. I got them running again (I thought) by wiggling and turning the wiper switch on and off, etc.

This behavior would rear its ugly head every so often, but not to the point where I was worried about not having wipers.

I already had a new combination switch in house to fix the broken "flash to pass" headlamp circuit and figured that this would also fix the wipers - if the problem was bad contacts in the switch.

Didn't drive the car for about 10 days, and when I got in it yesterday - no wipers at all. Washer works fine, but no wipers.

Replaced the switch today - no change. (Did get the flash-to-pass function back)

I'm thinking there are two likely culprits: wiper motor or the (I think it's called) combination relay under the hood atop the fuse box. Neither of these items is cheap.

Can't find any diagnostic charts in AllData - any suggestions?