from Wikipedia article about the Marxophone:
"Because the hammers are made of white lead, the instrument sheds small amounts of lead powder. Musicians who actively use this instrument have adopted the practice of coating the hammers in Epoxy glue, which does not affect the sound but stops the wearing away of the hammers (and prevents the poisoning of children, cats and other small creatures). "

I suppose new hammers could be made for an instrument.

Modern day usage: "The Marxophone did not become widely known to the general public, but recording artists have occasionally used it. The Doors, The Beach Boys, and John Prine used its unique sound on studio recordings of the 1960s and '70s and it is still used more recently including such notables as Norway's Avant-Garde artist Sturle Dagsland and American rock band the Stone Temple Pilots.

"The instrument was prominently used in the soundtrack of the BBC’s series Dirk Gently (TV series) "

The description says that "The player typically strums the chords with the left hand. The right hand plays the melody strings by depressing spring steel strips that hold small lead hammers over the strings." The photo shows someone with both hands on the hammer keys.