As you are already aware the original JBL throat sleeves were made of Bakelite and have become brittle with age and crack easily on impact when drivers are packaged/shipped improperly. In addition many of these drivers have lost their spec’d gauss making the magnet more prone to movement with impact thus intern cracking the aging brittle factory original throats. I see it all the time when these drivers are shipped! Compression driver value also decreases significantly with damaged throats. Here is a way make these drivers like new again. There is now a solution to have them repaired with a new sleeve. This is not really a DIY replacement as to do the repair properly the drivers need to be demagnetized/magnetized. I seen it done as a DIY but its not recommend as the unit will loose some charge when opened. There are other techniques of removing the throat without the need to open the driver but I do not have experience with this method. There are videos online describing the procedure.