The sleave must come straight out, as it is aligned to the camshaft with a keyway. I have seen the rotor drive piece brake during use, it's not common but it does happen.
I would suggest a good penetrating lube to be applied, and some gentle "tapping" to the piece from different angles. A very good product for rusted parts is Howes' Mirical Lubricator, I swear by it, but it may be hard to find. Drilling is not an option as you will damage the keyway. Be patient, some minor heat from a propane torch might help also, when the upper cover is off of course.
Hope this helps.
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop