I found a used, but not complete brake booster from a Ferrari 308 on E-bay, and with a spare in hand I tore into my old unit (and the new one).
First drew up a booster-splitting tool,
Worked like a charm.
On the inside,
The complete unit,
Pushrod removal tool. The push-rod is held in place by a rubber cap, securing a ball joint at the other end. a bit of lubricant in the hole and it pops out. takes a bit of force.
Internals layed out,
Push-rod with spring an poppet valve