In CS6 the extensions should still be listed in the extension manager and you would just have to check each of them to reinstall. I don't know how to remove just one manually.
You may be able to:
1) Rename your configuration folder to: configuration_all
2) Restart dreamweaver to create a new configuration folder
3) Close dreamweaver and remove eCart from the extension manger
4) Delete the blank configuration folder and rename configuration_all back to configuration
5) Restart the Extension Manager
6) Reinstall eCart