Unless you're having dramas with it, I would leave it as is. EGRs don't work at full throttle so don't affect power. Apart from reducing NOx, they actually increase part throttle efficiency by reducing vacuum and pumping losses. The computer is tuned with this function in mind so operates on the assumption that the engine is ingesting X amount of EGR at Y amount of throttle. Go blocking it and the computer won't know to compensate, but you'll possibly use more fuel due to increased throttle opening at a given load/rpm.
If you don't understand all that jargon, basically don't fuck with it unless it's rooted.
Sounds like the hot air intake hose... you can buy aftermarket replacements, from memory.
Crossflows with triple weber carby's, sound very close to the triple weber Hemi 6's.
Here's a few youtube video's -
I've also had a friends EF Falcon's brake booster fail. Luckily at slow speed in a carpark. Plastic brake booster housing had split.
AU series 2 onwards have the metal brake boosters FYI. Good upgrade as opposed to fitting another good plastic one. Interesting to hear it's a relatively straight forward modification to instal.
Glad you've got to the bottom of it and can enjoy (safely) driving your XH again.