Hi, Welcome to JustAnswer.com, I am glad you are here! My name is Eric & I will endeavor to answer your question.
OK, You have a mid 1980's Centurion... It seems like the safes we see that are 100 years old just seem to work forever and ever. We are however, seeing more and more of these 1/4 century old Centurions with similar problems. I'm going to advise you that your safe is just old. Perhaps seemingly prematurely so but nevertheless, the guts are wearing out. Tumblers wear. Micro tolerances gap causing jambing.
You need to have it serviced. A thorough cleaning & adjustment or possibly a rebuild.
There are some good locksmiths out there for whom this will be a walk in the park. If however, you get a guy (or gal) out to look at your safe who is scratching their head and saying "well maybe..." or "Ida Know" . Move on the next tech who can look at it and say with confidence, "I can fix that"
In any event it's a 99% chance that the issue needs hands on which I simply can't provide via the internet! Maybe some day...? But not today...
Happy New Year
I was able to get it open myself and feel your response was of no help.
Just saying it's old and needs servicing doesn't warrant payment.
Thanks for trying.