OK, I've just finished with some silver solder and flux. The 5000.2s standing on Herbie's Big Dots in my living room stereo system sound good. Not sure there's much difference from the original H539 tweeter, but I can stop worrying about ferrofluid for a few years...
Old dog... I assume that tag is literal.
I recently learned that I can’t hear much past 14kHz. Before everyone dismisses me as irrelevant, there is truly not much past 14 kHz having played test tones (as well as a lifetime of critical listening). We all have a slight ringing at complete silence.
This all said... I don’t want to be the bearer of bad news, but there is a slight possibility that you have lost the highest octave. But I’m going to assume it is that your old tweeters were in great shape. Mine were even older, being the previous model, so the difference was audible even to these well worn ears.
And that the comparison was to excellent Thiel tweeters, excellent Martin Logan AMT’s, and excellent Monitor Audio Ribbons...