X15 tractor vibrates when engine brake is on

[Waterloo]

I would at the very least get under the top of the motor and poke around, even a good visual, there may be something not tight or a broken bolt or worse rolling around in there.

And inspect the cam shaft lobes/rollers yourself. If there is something wrong under there, the dealer is going to try to blame you for the damage, so be prepared. We have all been there and done that. They tried the same with me and that in frame, when we pulled the parts and saw that they did not belong in my motor, well the tables turned.