Unlike Opemus 5 the bellows here are clipped on top and glued(?) on the bottom without an easy way to disassemble. Unless you have some kind of tool to help you unclip the top I would clean the whole assembly as one piece.

Remove focusing knob. Remove any oils or grime with appropriate solvent. Acetone worked for me. Be careful and always try solvents on the paint/surface where possible damage wont be noticeable.

Clean whole assembly in warm soapy water.

Dry as best as you can. Do not use blow-dryer on bellows!

Reapply grease and reassemble.