I'm interested to read that you have de-coupled the motor on the 401 but not bothered to do this on your 301. Is this because you don't think there are benefits to this modification?
I did a modification on my (heavily modified) Lenco which could be applied to our Garrards. I added a brace to the bottom of the main bearing which has a similar effect to stiffening the top plate. I have yet to try it on a Garrard but it was a positive addition to the Lenco.