Hi Fellas, I'm a bit of a Newbie here, but have been working on 45s for the past 9years (my own and neighbours).
My Red Rover 45 developed a real bad vibration in it and ended up replacing both halves of the motor clutch (Aluminium parts).
When I 1st got the mower the previous owner mentioned that it rips the clutch cork off the Cone section regularly.
What I found was that this has caused wear on the tapered surface of the Aluminium Clutch as well as wear in the motor side also.
It's a dream to use again now, after replacing them both for just over $50 all up.
Just thought I'd post another possible cause for Vibration, that maybe others are experiencing too.