The late Richard Carter of CASS fame told me he once had one that he wanted to get apart. The center stud is steel and gets rusted inside the bronze bell portion. The top cap screws off, then the bell slides on the center stud.
He said he "soaked that sucker" in some kind of solvent for about a year, and it still wouldn't budge! He was a machinist so he wound up drilling out the stud, then made a new longer one so a top brace could be added if needed. This one was on C&O 614 quite a bit on the NJ Transit trips in the 90's, as Rich was one of the crew from New Hope that maintained the 614.
( by the way, No. 90 at Strasburg also has a RDG 6-chime )
I hope to hear the one in the Chama shop on a C&TS engine again someday. Sure sounds beautiful in those great mountain echo-chambers.