Brake booster leakdown
 

I have an 85 300d with a few vacuum issues which a pump rebuild helped with but didn't cure. The tranny shifts much nicer now but still firm. My door locks take a few miles to start moving, but the engine seems to shut down consistently now. But the biggest problem hasn't changed at all, which is the draining of brake assist as you roll up to a stop. I could do panic type stops all day but as I slowly roll up behind a car at a light it's all I can do to stop. Sound like a bad booster? Other ideas? Is there a rebuild kit to correct this problem? I capped booster line and drove around with no assist and brakes felt fine (consistantly heavy of course) and everything else was the same. Any help greatly appreciated.
thanks
rob