I noticed a few postings regarding split-stems and I'm having a similar problem. Sorry if I missed the solution.
I'm working on a Hamilton "Electric". I may need to check again but, it appears it's an ETA 551.121. I removed the crystal and the back.
I was able to drop the movement out because the crown came off.
I'm concerned about pulling hard on the stem. I found a site that claimed you can slowly turn the crown back while wiggling ( http://www.mybulova.com/node/4602). I found this unsuccessful.
I've included a couple photos of the stem. I also noticed an arrow directly above the stem pointing to what looks like a release for the 2nd part (see black and white pic w/arrow).
I didn't want to depress the pin for fear I may have trouble getting things back together.
Any suggestions?
Dave.