3012 speaker distorting

[raytsmith]

One of my Jack 12's has developed some distortion. Sounds like a heavily cranked tube amp all the time, on all notes, even at low volume. The other Jack is fine, so its either the driver or the cab, and not the signal chain. They are straight bass cabs - no array, no filters, no casters, etc. And they are about 2-3 years old, the problem just recently started.
I've removed the grill, stuffed paper towels under the handles, tightened the jack plate, took the back off, took the driver out and shaved the foam filler a bit, reseated the driver, and reinstalled the back with more foam gasket around the opening. The cone appeared to be fine, no tears or dimples. None of the braces would budge when pulled on. Moving the cone by hand produced no suspicious sounds from the spider.
Next, I'm going to swap drivers and see if it follows the speaker to the new cabinet - but while its out, what should I check for to see if its a simple fix ? The surround and dustcap looked OK, but I didn't poke around on them very much the first time it was out - now I'm hoping there is something a bit of glue will fix.
Barring a quick fix, who repairs 3012 ho's these days ?

[BrentEvans]

Could be the crossover. Try driving the woofer directly from the amp, bypassing the crossover. If you still get the nastiness, then it's the woofer.

[Gregory East]

No filters.

All the same, you may as well try the suspect one out of the cab to see it it carries on before you go to all the trouble of swapping around drivers.