There was a grounding problem with the 700 wipers that was addressed by some by adding an extra ground wire to the motor. You should be able to tell if this has been done by removing the cowl plate and looking for that extra wire.

Also, the pivots can partially sieze and cause intermittent trouble. This is a bugger to deal with - you have to take out the whole wiper mechanism and push (or pound) the steel pivot shafts out of their cast metal pivot bodies and clean it all up. Use lots of grease on re-assembly, and new seals. Given the opportunity, I would install grease nipples and plan to remove the cowl plate and shoot in some grease every year or two.

If you find that your pivots are siezed, I suggest that you get a good used wiper mechanism before starting serious dismantling because you can wreck yours trying to get the pivots out. Wipers that don't work are even worse that wipers that may not work!