Greetings,
Cameras or lenses, my advice is send it to Canon for repair. If its older, (unserviceable) I'd try and find a good repair shop. Regardless of lens generation, hats off to you if you can pull off lens disassembly / reassembly on your own. I got hits for the parts on eBay, but I'd still want the service performed by someone who did repair as their business. I hope it works out for you.
~Rick
Bay Area - CA
~R5 C (1.0.7.1) ~RF Trinity, ~RF 100 Macro, ~RF 100~400, ~RF 100~500, ~RF 200-800 +RF 1.4x TC, BG-R10, 430EX III-RT ~DxO PhotoLab Elite ~DaVinci Resolve ~ImageClass MF644Cdw/MF656Cdw ~Pixel 8 ~CarePaks Are Worth It
