Where are the seals blown out at???
Find a salvage yard with some GM cars or even trucks(early 80s) with diesel engines in them...They will have the HydroBoost setup on them...
Or, I'm not sure because I've never checked, but they should offer a rebuild kit with the seals, etc., either at the dealer, or even aftermarket parts stores...Figure out which seals are blown, and replace them...Can't be any more than $5 or so per seal...
Herb is right, though, the HydroBoost setup is tough to beat for holding power...
edit
Just got off the phone with AutoZone, they had the HydroBoost booster w/o master cyl for about $121 + about $45 for a core charge...You would end up with that much in a vacuum setup swapping it over...They didn't have it in stock here, but could get it in about a day...Would have to pre-pay...