If the o-rings on the shaft are shot, the pressure from the manifold will leak past the seals and the ALDA won't see the boost.........even if you have it from the overboost valve.

This is a common and generally overlooked problem because it's very difficult to diagnose on the vehicle.

A boost gauge, when connected, will read low boost.........causing the owner to seek out problems with the turbo.

In reality, the turbo will make the boost if the ALDA wasn't leaking pressure and provided the fuel.

Testing the ALDA for pressure should be part of the procedure whenever "no power" is the symptom. It doesn't need to hold pressure completely, but shouldn't leak down faster than about three seconds or so. Any faster leak will cause a reduction in boost pressure to the ALDA.

Glad you found the issue.

Others should take note of this thread.