Quick test, put your mouth over the nipple of the actuator canister and suck, if you can stick your lip to the nipple with the vacuum then its an indication that the diaphragm inside is still intact - if you're just sucking gobfuls of funny tasting air in and creating no vacuum then there may be a hole in the diaphragm.

Personally i'm surprised you're using a -34 actuator on a T4, what boost control are you on? AMAL valve or air injector?

The other thing that may well be worth checking thoroughly before condemning the actuator is for boost leaks! Things like dump valves (Bailey ones in particular) can leak above certain boost pressures...