I would try an actuator first, as you will need one anyway if buggered if not make a nice spare.
Is there wear on the spindle that goes through the turbine housing ?
Physically grab(COLD ENGINE) the arm/spindle on which the rod from the actuator goes onto and see if it has any sideways play or up down movement.
The spindle part of this arm that passes through the turbine(exhaust) housing wears very badly, this causes the valve inside the housing which is just a round flat piece of metal that seals against a hole inside NOT to seal properly and so you lose boost, they TILT and normally crack the housing seat where they(valve) sits as well, but this is NOT necessarily bad, some can still be ok with this.
If wear is not too bad some can be repaired, if not it will need a new TURBINE housing, around £150 for T3.
If going to have it rebuilt, may as well go 360 and step gap at same time for a little extra.
The std bearing is a ring of 270 degree's but this can be changed for much better 360 degree one, essential if tuning though even std will not be very good with 270 bearing.
Step gap seal will help stop oil loss through turbo, by about 80/90%.
Speak to the TURBOCENTRE on 01924 404112, ask for ANDY or CRAIG.
tabetha