buy/ borrow a hand vacuum pump, apply 10 hg. in vacuum to wastegate (engine off) it should hold for at least 30 seconds without leaks. ( info taken from tech article for 86 svo) if it leaks it could be the wastegate actuator diaphram or a vacuum line.
i was looking over the tech page and that method is for testing the boost control solinoid, it was late and i was reading too fast, but it should work to test the wastegate actuator, it needs to stay open during vacuum.
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