MIMF

So, good thing i built this instrument in the first place so i knew what type of rod it was and what the geometry is.

Did the geometry to find out how to drill down to the rod under the steel bar.
I chose to drill at 45 degrees, and needed to be offset from the center by a bit more than 3/8".
Pulled the 5th and 10th fret and, marked the spot with yellow tape and carefully drilled in with a 1/16" bit in a pin vise.

Put my 100% silicone in a 3ml syringe with a 17 gage needle (i think - it has a 1/16" OD)
I was shocked at how easy it was to pass the silicone through the needle.

Stuck the needle in the hole, and easily injected 1ml into both locations. Rattle is gone.
After injecting, i cleaned up the fret slots and replaced the old frets. Going on vacation tomorrow, so leveling and re-setup will have to wait a week.
It was an easy job.
Thanks for the advise everyone, this was much easier than i thought it was going to be.

Well done.

Yay!

Love the photos, thanks for taking the time.

Thanks also for the photos, makes the description perfectly clear.

And nice inlay work, by the way.