Kubota BX 25: throttle stick slipping issue. Loss of rpm and power. 

I have noticed after I experienced the 'throttle down' issue, that others have also shared a similar frustration.
A bit of thought and a simple fix worked for me.
What I did not mention, the nut had not been tightened up at this point, and it is double nutted to maintain the friction setting. With a couple of additional spring washers and this metal plate, force required to move the throttle arm is still about the same as before the modification.