My used Magnepan 1.6's are missing sparkly treble. Why?

I recently bought a pair of used Magnepan 1.6 speakers.  Unclear how old they are but they appear to be in good condition and the panels look good when shining a flashlight through.  And the speakers sound good except they are almost completely lacking in that bright sparkly treble that I thought they were known for.  Something like  chimes or a triangle simply isn't in the music played through the 1.6's.  If you stand right next to the speaker you can hear those instruments very muted but not at any normal listening distance.  I've tried googling to see if this is a known problem with these old 1.6's but without any luck.  

Does anybody know what might be causing this or if it is fixable?
The fuses should never be bypassed. Asking for trouble. I hope your problem is something simple.
I think the previous owner did some unsanctioned surgery.
When in doubt, call Magnepan or email.
You could also call or PM Johnny Rutan (Audioconnection). He knows and sell Maggy's and might be able to give you some good (and free) advice.
Though he is a dealer, he is a really great guy who can help without trying to sell you something.
You can trust me on that...
Whatever it is it's bad and obscene. 
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You will probably have to remove that plate be to see how they were wired .