You said it works. Sandblast gently (not the rubber parts) and see if it reveals how to take it out. If not, lube it and leave it. Put screws partially back in before blast so that it does not cause a hole alignment issue. I'm sure several members know how it's assembled they just have not read your post yet. On other models I have worked on, the flapper being screwed to the shaft is what retains/traps the shaft. If that is the case, you may just need to lube/tap/turn the shaft and it will start to slide out. Maybe that's what Deve's site already says, I don't know.
