How to remove clutch master cylinder mounting sleeve

[johnk]

My clutch master cylinder has had a small leak so I intended to replace it while my car is in the rotisserie. Any idea how to remove the mounting sleeve that wraps around it?  There seems to be a rubber fitting between the cylinder and the mounting sleeve that I will damage if I can figure out how to separate. 

I tried putting it in a vice and spinning the master cylinder with out much luck.

Thanks
John k