wiper unit was need rebuild internal seals stiffen up with age.

Try pushing Marvel Mystery Oil or Neatsfoot Oil into the vacuum port of the wiper motor with an eye-dropper/pipette.  There is a seal inside that dries out.  This action will soften and swell the seal so that the motor works better.

Don't run them on a dry windshield. spray some water or Windex on, and they will move faster. Running the wipers dry can also make fine scratches in the glass. The main reason the vacuum wipers can be slow today is the 60+ years old grease in side the vacuum motor is very dried out and stifff like hard clay. It is  best to take the motor off the firewall, remove the top lid from the bowl, and clean it out good. Next put some fresh red disc brake style wheel bearing grease in. Also would not hurt to put fresh paper gaskets in.

To summarize the various actions you can take (starting with the simplest and cheapest and working toward the most expensive):

1). Try Christopher's suggestion with the Marvel oil or Neat's Foot Oil.  Get it into the wiper motor and then let it sit for a couple of days to allow the oil to be absorbed by the leather seal. so that it is supple. And also follow Ken's advice, and check the condition of the grease within the motor.  A good cleaning out of the stiff grease, followed by new grease, should improve the motor's operation.

2). At the same time, carefully examine the [u]linkage[/u] between the motor and the wiper transmission.  How easily does that work, once you remove the motor for cleaning?  Try lubricating the various pulleys until the linkage runs smoothly and without effort.  (I think the StepDown used cables; I have a pre-War model that uses steel rod linkages).

3). If that fails, consider sending the motor to a professional rebuilder like Wiperman.com.  It used to run $100 for a rebuild but it probably runs a lot more. The rebuilder can advise you if the motor casting has warped over the years, which means that it will no longer seal correctly, in which case you can look in Ebay for a N.O.S. motor.

4). The next step would be to consider using a double-acting fuel pump, which provides extra vacuum for wipers so they don't slow down on hills.  However, I've heard that these sometimes have internal oil leaks.  You might ask around on the Forum, what experiences other Hudson owners have encountered with double-acting pumps.