Sloppy steering

[Tone165]

Your service guy is an absolute pillock..
Don't go there again if he reckons a busa goes in a straight line because it has a damaged head bearing.

They are the most stable bike in a straight line that there is.

I think that he may have bled the oil out of the damper and not replaced it.
That is what I think.
He may also have not tightened the head bearing to the correct torque as well from what you are saying.
Go to Balls or Pete's Pitstop and get it fixed.
You don't need an aftermarket damper the OEM one is great when properly working.

Iagree with Busgo, sounds like your "mechanic" is full o shyte.

At least take it to the guys who list has reccommended for a decent diagnosis, and to get the work checked.