Few weeks ago I decided to order some new JBL factory diaphragms for my 4343 2420. I got the 2421 aluminium one. Yesterday with Mr Widget's help we did the replacement. Simple job you might thing. It was not that simple.
My drivers are in mint condition and were never open. I think I read here that the 2420 came from factory without any red seal. Mine do have seals but not the wax type but a nasty red glue that hardly dissolve with solvent. It took well experienced Mr Widget and I over an hour to open both drivers. One had a particularly resistant screw that didn't want to come out. So after an hour of battling Mr Widget won over the screw but lost a screw driver.After that it was easy to replace the diaphragms to center them and sweep tone test them. Will back home late I decided to reassemble everything and to give those new guys a spin. Wow! what a difference! it is really obvious that the old one sounded much more harsh. They were in really good condition, they looked like brand new but the 2421 are so sweet. I can't compare them to Mr Widget TADs which are amazing but I can say that now my mids do sound a little like the TADs. It's got the same openness and effortless sound. So my take here is that anyone with old compression driver should go the extra mile and spend some money on really good diaphragms, it's really worth it.
Thanks again Mr Widget, without you I would have never been able to open those guys by myself without destroying something.

Fred.