Remove motor and it's back cover to clean the contacts. Mine sometimes won't shut off but the cleaning seems to have worked. I had thought it was the relay but changed that too.
Since the motor does work and the intermittent wipe feature is controlled by the wiper relay I would focus on the this relay. I had a similar experience on my car. In my case I removed the relay and by shaking it I could hear something loose in there. I opened it up and sure enough a rivet which holds the solenoid in place was busted and the loose parts were creating havoc among the spate terminals at the bottom of the relay.
On my car, a 1972 3.0 CSi, in the fuse panel area on the left inner fender wall. It's a black box 1 1/4-in wide x 2 1/2-in tall and 2-in deep. The writing on the relay is Wisch-Wasch-Intervall-Steuergerät. It has a 6 spate terminal on the connector plug and one external spate terminal. It's mounted vertical and simply pulls out (towards the steering column) from the mounting bracket. I found my replacement relay on eBay for $95. You also see a picture of the relay there.
http://www.ebay.com/itm/221271860078?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
http://www.ebay.com/itm/221271860078?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
I have a spare relay if needed.