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?