When I was putting the Mueller back on the TC today, I felt something rattling inside the scope. The noise seemed to be coming from the eyepiece area.
To make a long story short, I unscrewed the eyepiece and found that an internal lock ring had rattled loose, allowing a thick lens to rattle around inside the eyepiece.
I also noticed that the inside of the scope was extremely dusty.
I cleaned it up as best I could, snugged up the internal lock ring, and now the scope is back to normal with no rattle.
Whatever nitrogen was inside has probably escaped but I'm not convinced it was ever air-tight to start with.
I'm guessing the tremendous recoil of the 357 magnum
had loosened the internal lock ring. I applied a tiny dab of sealant to the lock ring so maybe it'll stay put this time.