mal ... DON'T.
I got a replacement Dreamcast lens from Lik-Sang.
Didn't work.
Sent it back, got another one.
Didn't work.
Some experiments with both of my DC consoles and a lenghty e-mail exchange with a nice Lik-Sang rep lead me to believe there's an incompatibility of some sort between the kind of lens they sell, and U.S. Dreamcast consoles. Oh, and mine have a Yamaha and a Sanyo GD-ROM drive each... made no difference.
The problem I has was the laser would move up and down but not emit any light whatsoever.
So... I just want to save you from some trouble and frustration. You might be luckier just getting a whole replacement GD-ROM drive, which shouldn't cost much more...