Bingo! I just finished putting my new to me C9.25 back together. It had the classic symptom of not holding collimation and not holding focus after slewing. I suspect that this scope has never been taken apart as there were spots of fungus on the inside of the corrector and the corrector was really stuck! I marked its orientation, sprayed around the edge with Windex, and carefully worked it loose. I reached down inside and engaged a wooden dowel with one of the spanner holes in the lock ring a nudged it. Sure enough, it was completely loose. I could turn it about 1/2 rotation without any resistance. Just a tad more, and it was snug. While I had it open I removed a few tiny spots off of the primary and secondary with lens tissues .(I _hate_ touching the mirrors, but sometimes you get lucky) The secondary also have a bit of fungus, now clean. I carefully cleaned the inside of the corrector with Windex followed by breath and lens tissues. Before closing the tube I inverted it and used a puffer bulb to blow the dust out, and then carefully lowered the corrector back in place. I didn't like the original tiny spacers, so I cut ribbons of black construction paper and layered them evenly around the corrector until the gap was full (about 5 layers total all the way around). I remounted the rail, reinstalled the finder, touched up the paint, and now it's ready for testing.
So far I'm 3 for 3 finding loose lock rings. Tomorrow I'm going to open up a 12" that's showing the same symptom. Gotta do something while its cloudy.