I have had this same problem with the wipers ending their cycle in the up position, a number of times. Very frustrating. What I finally did was take the shroud off above the wiper drive shafts and then take the plastic cover off the top of the cam assembly. It just snaps off. You will notice (when the wipers are running that the cam rotates once each cycle, and when the wipers shut off, there is an intermidiate plate that is suppose to slide part way around (about 90 degrees), independant of the upper plate, extending the plate forward, thus pushing the wiper arms down. It seems that it needs to be lubricated for the plates to slide and do their thing. How to accomplish the repair? Magic. Actually, I first disconnected the wiper push arms from the cam and then just fiddled with the cam unit (you must have the right kind of screw driver head; 6 pointed star), moving it alittle and turning it alittle and somehow (I don't recall), it suddenly released the inner plate and extended. ***OH YES, THE CAR WAS TURNED OFF AT THE TIME***. I lubed it up, put everything back together and it works fine...so far.
Time will tell if I screwed it up somehow, but so far so good.
Mike