The foam surrounds on the bass units are completely gone.
The great news is that it's inexpensive to fix. There's some youtube videos showing you how to replace foam surrounds.
I found it an easy job on mine - apart from gluing the foam to the right place on the cage. There's a high chance that you shouldn't glue them centrally as you look at them, and that you should glue them offset by a millimetre or two. My technique was to press the cone in and out with my fingers to find the positions where it was rubbing and the position where it wasn't. And then to carefully glue it in the position where it doesn't rub. There are other techniques you can use such as scalpelling the dust cap off and using a card spacer to get the right position, but I wasn't confident that I could glue the dust caps back down neatly again.
I suppose the thing to remember with a refoam job is that if you get it wrong, you just take the new foam off, buy another kit and start again. A foam kit for a pair of speakers will cost you £35 give or take a bit. Use Google or eBay to find sellers.
Whilst you've got the bass cones out you could have a look at the capacitors in the crossovers. If they're bulging or have leaked fluid I'd replace them.
If you think they sound pretty good now, just wait till you get the foam surrounds replaced. And you can expect another 15 to 20 years use out of your lovely JBL's without further maintenance.