Sorry to air my obsession with this tapeset again, I was watching this video of Hessel's:
There does seem to be something different about the sound of an M300 as opposed to an M400 playing the same tape set, but I can't put my finger on what it is although that has always been the mellotron sound I wanted. Unfortunately the sound of my M400 has always been a disappointment I suppose there is quite a big difference between a Mark II an M400 and a Chamberlin playing the 3 violins.
This link is to a little demo on my Soundcloud channel comparing the sound of my M400, the Streetly samples of the M300a from M-tron Pro and the M300a samples in Redtron SE. I am not going to buy an M300!
Mark
PS If anyone knows why the M300 sounds different I would really like to know.