[codefox1]

Could be a bunch of crud on the thread of locking screw, blast it off with deoxit. If clip is removed, see that there are no bent members below chassis, including soldered to tabs, don't know, unfamiliar with this model. Whatever, go slow, agree you should unsolder and document connections. BTY get a little digital camera that can do macro to record your progress. Cheap enough, and worth their weight in gold.

Sometimes there is just an accumulation of wax and other stuff that needs to be "broken" to free mechanical connections. Not a science but an art. Gently probe this possibility.