A couple of years ago I added some reinforcement to my Gibson B45 12-string guitar. A JLD Bridge Doctor was part of the fix, but yesterday it broke. I'm not sure why...I had medium weight strings and had the guitar tuned down a fourth. The tension was really too sloppy, rather than too much.
Here is a link to a series of pics snapped during the project.The JDL Bridge Doctor is that piece that goes from under the bridge to the tail of the guitar.
I really like the sound of this guitar. It is unlike my Taylors in that there is very little mid-range or sparkle. Very old-fashioned (think 1930's era).
I expect to open it back up and do some more surgery. I'm thinking of attaching a permanent piece to the underside of the maple triangle and bridge back to the tailpiece but using solid, non-adjustable thing-a-ma-jigs. I haven't worked out the details yet. But the JDL didn't keep the top straight and it was very hard to keep in tune as the bridge see-sawed from playing.
I'm also wondering about making the top two courses be single strings. It seems odd that 4 courses are octaves and two courses are unisons. Doesn't make sense. It's harder to play tremolo or arpeggio with any speed on a double course.
You can buy Bridge Doctors at stewmac.com, among other places. They are simple to install, but you do have to drill a hole in the bridge.