W3C Validation & HTML Editor

Hi my boss is wanting all our sites to be fully W3C compliant which isn't a problem but most of the errors I am correcting are down to HTML Editor for instance W3C want a return to be <br /> if i change this in the editor and validate everything is ok but if i go back and alter some text the editor reverts back to <br> making it none compliant.

I also have the editor using mystyle sheets which again is great but, if for instance i have formatted my test using the default font size etc of the editor then restyle with my style sheet it will view correctly on my site but in the source of the text in the editor it is leaving the past styles in as well creating extra code that is not needed and causing it o fail validation.

Any tips or help with this will be much appreciated thanks Alistair