Thanks, Steve
All errors are entirely my fault!
Actually, listening to the tt this morning, it sounds noticeably more together than with my previous bodge-up with the 2p pieces blu-tacked on the end of the standard Techie c/w.
But I think I will take you up on your kind offer and return it for the internal 'sleeve' you mention, also an added bit of weight would be fine, too, as the c/w is riding toward the back of the shaft.
Also, is it possible to add an extra grub-screw about 2/3rds of the way back on the c/w? Otherwise it can wobble a bit if the fit isn't perfect.
Happy to meet your parts and labour costs on ths mess-up, of course.
Can you just drop me your address by PM.