90Q brake question

["Vlajko Jokic" <vlajko.jokic@sympatico.ca>]

An excessive pedal effort is required to stop my 1988 90Q. I think that power
brake booster is gone. If the pedal is depress while the engine is running, and
then the engine is stopped, the pedal would rise instantly, pushing my foot up.
Also, when engine is stopped (without having brake pedal depressed while 
running), and then the brake applied, no signs of booster airtightness, ie., 
that pedal feels too hard  as the engine was not running for hours. 
Remaining vacuum seems to be lost instantly if the engine is not running.  
Finally, if the pedal is strongly depressed while engine is running, I can hear
air
leak noise coming from the place where pedal is attached to the booster.
Is my booster really mulfunctioning? 
Would a mulfunctioning ABS unit make a simmilar effect?
Does anybody know is certain seal replaceable inside the booster, or I have to
replace whole unit? Some information about price would be very helpful, as
well...  Is this unit maybe the same as one on Golf/Jetta?

Regards,

Vlajko Jokic
Canada

88 90Q