If your power steering works very well replace the hydroboost unit
If the steering is also having assist issues replace the pump and retest the brakes and hydroboost
The procedure is similar to a normal vacuum booster to replace
Just unbolt from the pedal support and the master cylinder and the 2 power steering pump lines and then it self bleeds like a PS pump
Elevate the front wheels and 20 turns of the steering wheel lock to lock (do it slow) until all the air is out
Take your time ( I usually turn it one way and wait a few minutes then turn it the other way and wait a few minutes)
After you do that a few times, then you can start turning it back and forth and wait some more
I replaced my hydroboost unit (along with my master cylinder) on my 2002 GT back in 2016. It really wasn't that difficult. Just follow the instructions above. I was able to get a brand-new Motorcraft hydroboost unit on Amazon for not too terrible of a price.
I discovered mine was leaking because my power steering pump started whining from low fluid level, and there were no leaks at the rack. I didn't replace my power steering pump (until last night, but that's a part of a 3½ year long project on my car, where it's been up on jack-stands in my garage all that time!), but it was fine.