I have a wico magneto model xh-184.I tried to get the screws off so I can remove the cap and see if it salvageable but they are really rusted out and will not Budge.Any Opinions thanks in advance 

Try heating the case with a small propane torch. Just where the screw is, a few seconds. Let everything cool off. Do this many times. Soak with PB blaster or equivalent. Gently! try to turn the screw. If it doesn't move, start the heating cycle again. They may come out. The other alternative is send the mag out to be repaired. Just my .02 on what to do. Good luck.

sometimes after letting a penetrating oil soak for a while you can shock things loose buy applying a bit of force with the screwdriver and tapping the screwdriver gently with a hammer.also try tightening gently first some times they will do up before they undo

Greatest invention ever for motorcycle mechanics: The impact screwdriver. Just take it easy. Steel screws into aluminum or white metal "weld" themselves in. There is an actual exchange of molecules between the iron and salt metal.

Another method of applying heat is to heat up a steel rod red hot and touch it to the case over the thread. Don't go hot enough to melt the case. Then stick the whole thing into cold water until it's cold, pull it out and heat again. Don't start on this until you have time and patience to see it work, if it's going to. Work first one screw, then another until you find the easiest one. Then you can reasonably judge what you are up against by looking at the threads. If you send this job to a mag rebuilder, he might just bust off or drill the heads and sell you a new case. The bill for services of this type can get horrendous if it takes a long time. Do whatever you can first.

Not salt metal, it's soft metal. How do you shut down that d++++++ spell checker?

I've went so far as drilling the heads off the screws/bolts, removed the cap/cover which gave me much better access.
My smell checker is twerking just fine.🤣😂🤣

yes the heating a bit of rod would work well so would a soldering iron. yet its strange brass and bronze nuts dont seem to weld on to steel yet steel into brass will seize in place must be due to the fact rust expands.