In my 1986 F250 4.9l my brake pedal is hard and when the engine is running it won't return. I suspected my brake booster. When I unbolted the brake booster I found that there was brake fluid that's leaked into it.
So, I assume my booster is shot.

My mom's boyfriend has a 1987 F150 that's been setting in his yard for about a year and a half. Would the brake booster out of it work on my 1986 F250? If not, would the booster out a junkyard truck most likely be seized from setting?

 

The parts book says the F150 & 250 under 7000 GVW used the same booster (E4TZ 2005-A) at least through 1989 (where the book ends).

 

That brake fluid got in the booster from the master so it needs to be replaced also.
Dave ----