From my reading on the subject it appears the single LED boards have a much higher failure rate than the other boards. But any of the lamp boards in the game are subject to failure. They are a known problem - especially the older 5v system like I have.
This is why I am really really hoping JJP developing a kit to upgrade older machines to the new WoZ 2.0 lamp system which is based on the system used in The Hobbit.