With PCboard removed, you have full access to the ring and PCBoard contactors so I see no reason to dismantle more than that. Just ensure the sprnged contactors do make contact woth the ring and this should ensure wipers returning to park when turned off. I do not have exactly the logic but I think the wiper switch (through the pcboard logic, timed pulses, etc) just excites the small segment that takes the wipers off park and from then on, the wipers continue the full cycle back to park from the long segment. IF at some place the large segment looses contact, wipers stop in the middle of the run.
On return to park, if small segment is not excited then wipers stay there (parked) but if small segment is excited, it passes out of park..and then again receives juice for the rest of the cycle from the long segment..and repeats. So I think the long segment contactor can be the problem...or some cracked solder linked to contact plays tricks.
PCboard is known to be a really common source of problem, there have been dozens oc ocurences on this forum and other GM products so I would not rule out redoing the solders or ordering a replacement on Ebay.
Mine has restarted playing tricks recently and I'll redo the soldering again; honestly, last time I did it, I needed a strong magnifying glass to really see the cracks..so I remelted as many solder points as I could...., that was less than 2 y ago.