Three screws at the back is easy enough. Problem is the adjusting knob going through the clear plastic front. I have the tiny screw out covering the end of the hollow chrome stem and little knob which is one piece. Inside the stem is the shaft that won't come loose. I have a drop of WD40 in the tiny top hole, should i let it sit for a day and then give the end of the shaft a light tap or is there another way ?
Chrome stem and knob is one piece. Inside is the hidden shaft. Can only see the end point. ( red arrow )
Now that I look at it again, I kinda agree with what 302GMC suggested; as having the stem & knurled knob as one piece doesn't lend itself that well to manufacturing. If you can see a small nub inside the knob, that's probably the end of the stem. Can you determine that using a magnifying glass? Regardless, there should be a way to disassemble the clock to service it. Originally, it might have been tightened very tight onto the threads. Try some PB blaster or Kroil and let it sit awhile; then try the pliers trick.
One thing I’ve found useful for things like this is searching for the part for sale on eBay, there’s usually some good pics that may help. https://www.ebay.com/itm/374724085130
Got it loose this evening but it was a tough one. With the three screws on the back removed i could jiggle the clock around a little to get a 1/2 inch opening at the backside and a good look at the whole chrome stem. Well it was green in there with oxidation right on the joint where it should separate . Now i figured try to heat the stem but how as the front clock lens is plastic, not glass. Soldering flux and just held the iron in there on the stem joint until i could,nt hold the steel frame anymore. Did,nt work, still stuk solid. After some choice words as in "pardon my french " i began to wonder why is there a small hole in the head of the tiny screw/stud. Then it hit me, put it in the hole backwards and it fits on the end point of the shaft, not the thread. Now some pliers behind the chrome head of the stem and press. Popped loose at once, now i wonder if the heat helped just a little.