My DC H10-40s are at least 20yrs old. I bought them from my CPL instructor in 84.
They used to have a problem with the plugs (old style, unscrew to the plastic surround), & I had a mike & speaker unit fail. I had replaced the rivets that mount the earcup stirrup to the headband with bolts, bushes & locknuts when one failed.
Sent them back to DC in the USA in 93 or 94. For US$70 they refurbished them. New mike, all new leads & plugs, new head band & cushion, new earcup pads.
About the only parts that seems to be original are the earcups & mike boom. Maybe the good speaker but since then I've never had cause to pull them apart.
They would have installed a volume control but I asked them not to. Just something else to break, IMO. Especially when there's already a volume knob on the radio...