Tricky one
The only sure way to do the job properly is to remove the transmission, gearbox from rear, engine and bell housing to front.
Then you can access the clutch sleeve easily , get it freed off, cleaned up and the bell housing machined and sleeved to prevent it happening again.
You can try all sorts of release agents into every orifice on the bell housing and gentle heat, but ( I hope I am wrong) with only a limited chance of success.
If you do decide to remove the transmission , come back on here as there are several tips that you easily make use of , to future proof the work
Good luck
