The best upgrade you can give any SCT is a feathertouch focuser
In good condition
Starlight Instruments Feather-Touch MicroFocuser for use with Celestron C 11 SCT, CPC-1100 and C11 EDGE HD.
Replace your telescope's standard focuser for this Starlight Instruments Feather-Touch MicroFocuser for smoother and more precise focusing.
Dual-speed mechanism with two focus knobs. One provides standard speed focusing, the other features a 10-to-1 reduction unit for extra fine focus.
Starlight Instruments products and accessories are precision machined from the highest quality materials to insure long life and trouble-free operation.