Geoff (Newcastle, NSW) replied:

Hey Al,
Is it possible for the manifold pressure to rise above atmospheric?

Maybe there's a gas leak that is pressurising the manifold and up the vacuum hose thus breaking the booster?

Maybe so far off the dial here but hey, you are looking for way out suggestions.

Geoff

Martyn (WA) replied:

Al,
Bit out there but there is a ever so slight amount of residue in the LPG that attacks the plastisisers in rubber compounds which casuse the rubber compounds to breakdown and fail, happens with the cheaper hoses on cheaper gas conversions. There isn't I don't think an AS standard yet for gas conversion components, I know there will be one soon if there isn't already. If the damage to the booster looks like rotting rather than ripping you may have a faulty component that is allowing more LPG to get into your booster circuit. As I say a bit out there but you never know. personally I haven't got a vehicle with an LPG conversion it's just something I've heard around the traps.
My opinions others may vary

Fatman replied:

hey bro, i got an idea bro... go down to your local petrol station, buy a jerry can full of petrol (not diesel bro) and a box of matches. i'll let you use your imagination bro

donks1 replied:

hi there

eb to ef falcons had an issue with excess heat from manifold being too close to the booster. this used to melt/distort the diaphram in the booster. you may need to make a heat shield too stop it happening again

donks