Brake pedal hard

[FourPointEight-is]

I seem to have lost about 80% of my power brake assist in my E53 4.8is. The car will still stop but I have to REALLY stand on the pedal to get any braking at all, it isn't effortless like it used to be.

If I brake gently (like coming up to a stop sign or lights) the pedal still feels somewhat "Normal" for the first 20% or so of its travel, but then suddenly the pedal becomes very hard - like I'm trying to compress wood. The brakes still work but require considerable effort to apply.

If I brake hard (like an emergency stop), the pedal goes down "normally" but then it suddenly firms up and kicks back against my foot at which point it feels like I'm trying to compress wood. Again, applying considerable effort, I can stop the car.

When stopped, I am having to apply considerable force to the pedal to keep the car stopped. I also feel a slight pulsating coming form the pedal as well (but its barely perceptible).

Does this sound like a brake booster issue? From the reading I've done there are recalls out for brake booster/vacuum line/check valve on the E70 X5s which share the braking system (parts and all) with the E53, but apparently E53 4.8is are not eligible?

Follow up question - if I need to replace the booster, is it worth also replacing the master cylinder or am I safe to reuse it? Is it possible to recondition the brake booster or is it a "throw away, get new" type part?

Lastly, if I replace the break booster and/or the master cylinder, I guess I need to bleed the whole system. Will ISTA be able to do this for me? If not which software do I need to do this?