ok, sorry for the delay.
I believe you can replace this O ring without removing the housing it goes through. Undo the 2 lock nuts that hold the lever in place. Remove the washer on top of the arm, now, you will need to try and lever the arm off the shaft, it has a key to locate its self. Once you remove the arm, remove the key from the shaft and remove the large washer under it, you should see the O ring under that, oil the O ring before installing it. Re-assemble in reverse order (of course).
The shaft may have some slight movement downwards but it should hit the timing cover housing, so it will not drop all the way down.
If you have any questions just yell!