Help removing an Atrium lock set

A home owner from Florida says:
I have a 35+year old door with an Atrium Mortise Lock set. It no longer functions correctly and I need to replace it. I had it almost totally torn down with all wood screws, machine screw and such removed. I could not remove the second screw from the bottom on the door edge side. You called this a set screw in another question. I back out the stew to a certain point and then it freezes. Some threads are visible, but is does not seem like it wants to come any more. I do not want to break something. What do I do to remove the set screw and then the entire lock?
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Dave Sr. from SWISCO responded:

I believe what you're talking about is the set screw at the bottom edge which secures the key cylinder in place. I suggest using a type of spray lubricant like WD-40 spray it into the threads. Also, while unscrewing the set screw, try to "jiggle" the key cylinder at the same time. Maybe that will help free up the screw.

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