Found a service bulletin regarding mushie brakes.
I'm going hydro, have all the arts, but the cost even from a wrecker is still more than buying this doohick.
FWIW:
"
1997 and earlier diesel trucks equiped with vacuum power brakes--
Low/creeping pedal:
Many owners have complained of a low or creeping brake pedal on their trucks, often mistaken for a bad master cylinder or Rear ABS valve. If the condition occurs after the vehicle has come to a stop, and
no other brake concerns are found, (worn or out-of-adjusted brakes, cocked pads, or hydraulic problems) the condition is normal and the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds it unacceptable. This part is
only for use on diesel-equiped trucks--P/N F5TZ-2005-CA--and is not a service replacement; it must be ordered by the part number, not vehicle application.
This condition is similar to the low brake pedal concern on all 1995 F-series that required a larger-diameter master cylinder."
Can order one from here:
http://www.fordpartsgiant.com/parts/ford-booster-asy-brake_f5tz-2005-ca.html