I bought a pair of these a few months ago on Ebay. Unfortunately one of the drivers was damaged, only outputting weak distorted sound. I have searched in vain for a replacement driver (38-701F) to no avail. I'm pretty sure these are not available anywhere, no NOS or alternative. The only option is from a donor pair, but as it is pretty much the only thing that can go wrong, they just aren't anywhere to be found.
Anyway, I decided to have a repairing it. Carefully and slowly working around the edge of the diaphram with a tiny screwdriver, I managed to release it. I could lift the voice coil out of the magnet and leave the fine wires connected.
I cleaned out the gap with some double-sided sticky tape on a sliver of fine card. I found quite a few small fragments (see the picture in between the screwdriver and tweezers) in there which would have been causing rubbing on the coil. After cleaning I added a small drop of ferrofluid in to the gap and glued the cone back on with a single layer of evo-stick. Disappointingly, the sound was still bad.
Today I disassembled it again cleaned one more time, but this time I didn't glue the cone back before trying it. Great full range none distorted sound. I think the cone was too tight or slightly off line the first time, being loose allows the ferrofluid to do it's job and hold the coil away from the magnet. A very small amount of the remaining glue is holding the cone lightly and stopping any buzzing.
Very pleased as up until now they have been useless, or destined to become someone else's donor-pair! I would say, I you have this problem it's worth a go, nothing to loose! The design of these headphones means it it fairly easy for small particles to get in to the coil gap (ie anything smaller than the mesh gap on the outside of them). Obviously all wiring connections etc., should be checked before doing this.
Sound great by the way, and surely some of the best looking headphones ever made!
Dan