JBL L5 - Frozen Voice Coil (Woofer)

Looking for some advice on why I currently have a frozen 8" woofer voice coil on my JBL L5s. I'm not sure if there's an electrical/impedance issue with my amp or if I just pushed them too hard, or if something like this can happen just due to age?

I have a fairly new Luxman L-509X integrated amp and my main speakers are Klipsch La Scala IIs. Short version is I sent a burst of digital noise through the La Scalas a couple weeks ago and blew a tweeter diaphragm. 

While waiting for Klipsch warranty repair (they are 5 months old), I bought a used pair of JBL L5s off Craigslist. At $400 they were a good deal and up until tonight were enough to get me by until the La Scala IIs were back in the game.

BUT tonight I discovered there's a frozen voice coil on the right JBL bottom woofer. No sound, the woofer is just frozen and stuck out. 

I am guessing on a 25 year old pair of speakers like these, I'm just out of luck when it comes to repair. My bigger concern is what may have caused this. They were working fine, have not been dropped or otherwise mishandled. 

I am using a vintage Luxman CL40 valve preamp occasionally in front of the L-509X (using the HT bypass function). Is it possible some kind of DC is leaking somewhere and fried the voice coil on the speaker? I'm not even sure what that means but it sounds scary and detrimental to my $$$ gear. 

OR is it possible I just overpowered the JBLs with the Luxman gear? I have been listening to some bass-heavy music recently at about 102 dB, so at the JBL's rated 90 dB sensitivity at most I guess I was pushing 50 watts into the speakers? 

If the JBL is toast, so be it (I don't want to put any more money into them), but I am very concerned about any power issues once I get the La Scala IIs repaired.