I've just finished adjusting the counter in my Retina. It's now working beautifully. I watched a Chris Sherlock video to see how to remove the top cover, and the advice here on this thread to adjust the counter. It required several full turns of the screw to get it down to a single step advance. I have no idea how it got out of adjustment so badly. I know it wasn't anything I would have done.
The hardest part was actually getting a screwdriver blade into the end of the screw. My old eyes, even with glasses, were no match. I had to resort to a 10x loupe just to be able to see it clearly. Once engaged, the screw was easy to turn.
I want to thank everyone here so much for your generous advice and pictures. It saved me a lot of trouble and grief.
Yous guys are da best!!
... and of course, kudos to Chris Sherlock too for his amazing series of camera repair videos on YouTube!