Like Geoff, I found that to get the necessary leverage, the best bet was to undo the 3 bolts that secure the diaphragm bracket to the turbo impeller housing (the shiny aluminium bit).
This then allows you to move the whole diaphragm and rod from side to side, which soon has it running silky smooth.
The only problem is the bottom bolt (nearest the wastegate actuator rod). Ideally you need to curl your arm right underneath by snaking it down past the water pump.
If you haven't done this, then as Geoff says, there could be more than one point of resistance.
Here are a few pics - I've just been cleaning up my spare turbo. Ignore the join in the wastegate actuator rod - it's decidedly non-standard, but helped to get it out of the way for the purpose of these photos.



