If your having trouble with poor wiper strength, particularly if they're struggling on the return stroke, you might be interested in this!
I fixed my trico vacuum wiper motor the other day so I thought I'd post the story. You'll see a part I've highlighted in red in the pic. It's a small part in the reversing lever assembly. At first I couldn't find the problem becuase this part was only cracked and not fully broken, so it looked ok until further inspection when I saw it bending instead of doing it's job, which is to facilitate in switching air ports so the wipers return properly. This part seems to be made out of some sort of old plastic or something, without it working properly the airflow inside the wiper motor is poor to non exsistent. So I made this broken part out of 1mm aluminum plate, put everything back together and have got my vacuum motor working like it just rolled out of the factory.