I would completely disassemble a mandrain (key) to drill, which for the changes in diameter to be clamped, hard to turn because oxidized/dirty.
By thoroughly cleaning piece by piece, after winding it should work again by turning freely without forcing.
I disconnected from the mandrain the perÃ§euce, but I do not know how to disassemble the mandrain for cleaning all the parts separately. If you have the user manual, can you tell me what to do. Thank you in advance for your help.