My actuator has almost 5mm of preload, the stroke of the thing is huge.
The hole Craig is talking about is the hole in the Wastegate arm, that the pivot pin goes through.
Boring out the Wastegate isn't going to make it hold boost better, if anything; it will allow you to bleed boost pressure more easily.
It would be worth doing if you were building boost pressure uncontrollably, but you have the exact opposite issue.