The Lotus Elise/Exige marker lights suffer from broken posts that attach it to the clam. These plastic posts can snap when an overzealous hand tightens a bit too generously. Replacement parts are getting harder to find so repairing your broken part is often the best option.
Carlos has come up with this great idea that will allow you to fix your light. The basic steps are as follows:
Cut off the broken post - flush with the base
Drill a hole where the post was located
Use a coarse threaded screw with an appropriately sized washer to attach the light to the clam
Please see the picture below for better clarity on this tweak.