Heidenhain Encoder 450 problem

Looks like I have a problem with the Z encoder , its showing Im over the limit and wont correct itself even though I have moved the Z by hand and think , after taking the Heidenhain 450 Encoder of the end of its mounting on the shaft that it has a lot of oil gatherd in it and maybe seaped into the sealed unit covering it in oil ! Not Good ! My question is is the cover glued on to the unit ? And if its possible to take the cover off to clean it up ?


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