Try this guide of ebay.
http://cgi.ebay.co.uk/Denon-UD-M30-UD-M31-How-to-replace-a-faulty-laser_W0QQitemZ260383613591QQcmdZViewItemQQptZUK_AudioVisualElectronics_HomeAudioHiFi_CompleteHifiSystems?hash=item260383613591&_trksid=p3286.c0.m14&_trkparms=72%3A1300%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318
Andy Francis, March 2009