The one you have runs on vacuum from the engine???
The internal seals dry out. Here's a photo from a 'not a Ranchero'.
If you can get some brake fluid run thru the insides it helps rejuvenate the seals.
At this link...
https://www.ctci.org/improving-winds...iper-function/
There are rebuilding services available, approx $135 plus $200 core charge.
Although this one may/may not be T-bird specific???
Call them and ask to confirm.
https://www.classictbird.com/Wiper-M...uctinfo/17508/