I'm looking for some help with ideas regarding my wipers on my '78 f150.

I've been working on my rig I inherited last year. It sat a long time with moisture getting in the cab. I've replaced the head light switch, wiper switch, and replaced the crumbling cluster plate/circuit. Lights seem to be all good now, instruments all working, but the wipers are an issue again. When I got the rig, only the fast speed worked (has intermittent) and the intermittent was REALLY intermittent. I did the switch last November and things were good. Now that I rebuilt the instrument cluster last week, the wipers work well when I start up, but sometimes stop working on intermittent and normal speed, but the fast speed always works. Then out of the blue 10 or 15 min later, it all works again. I looked at the motor and it appears dry and not corroded, and all the connections seem fine. I redid the ground, putting lock tooth washers in between the 3 ground lugs and dielectric grease on it to boot.

Any thoughts on what to do next short of replacing the motor?

Thanks in advance for your advice.

Ken