Hi John. Same problem, steel and alloy screwed together for 60 years...You could try removing the parts, place one as a test, into mild citric acid which will clean the rust and scale out. Your local swimming pool shop sells "Black spot remover" which is just 100% citric acid crystals. Add citric crystals to water then add your part and keep an eye on it. Should take 4-6 hours to clean it up without damaging the parts, repeat if required.
This method of citric cleaning is used with caustic as a neutraliser but in this case your side lights contain alloys, which caustic will eat in minutes.
This is a museum conservation method which is a variation on the old molasses process. Citric takes hours to do its work where molasses takes weeks, same result.
Canadians do have swimming pools shops? Swim in your pool in summer then skate on it in winter...
