Record power have a good knowledge base on their website which might have the answer. If you register you can then email the problem and one of their guys will get back to you.
http://www.recordpower.co.uk/index.php? ... =16&dp=114
This is one problem i found with my cl3. The inner grub screw securing the pulley block had loosened.
After changing the belt, spindle and bearings I still had vibration problems.
In the end it was the tail stock quill. The barrel had worn in side and gone oval giving support to the morse taper at a couple of points instead of the radius of the barrel.
Contacted record via the website and spoke to Tony Rhodes who promptly sent me out a new barrel free of charge. Excellent advice and service.
There is a download for the cl3 manual on the site but I can't see one for yours but ask them, I'm sure they can help.