If I hadn't been able to do this bulb fix, the next project would have involved grinding away part of the original bulb holder so that it would accept the 13139 bulb. I REALLY didn't fancy doing that so I'm glad I got it to work! Thanks for pointing out the difference between the 6604 and 13139 bulb. It confuses a lot of people as you can see in this thread so it's definitely worth repeating.