[FrankB]

Boy that is an oldie!

Check gearbox for grease. Maybe even wash it out and re-lube, looking through the old grease for any possible broken metal bits. (That age they used a gearbox, based on the one similar to that that I have. Likely hi temp dish brake grease would be fine.

Look for worn bearings or a shim gone bad.
Check to see if it has an oscillating function. I had one that rattled like that because it was not fully disengaged.

Bearing wear would be next. I did have one similar and it did have bad bearings. Being unable to find any, and not having a metal lathe at the time, I used shim stock (brass?) at the time, but made sure to lube it every month.

A really out of balance blade would cause a lot of continual vibration. I do not think blade balance is an issue, but you can remove the blade assy. and balance it on the end of a large needle to see if one side is heavier than another, or a blade is bent.

Make sure the blade guard is tightly attached. They can cause some really odd rattles.

Also check the fan to base joint for play.

Collecting old brass fans has become quite a specialized hobby here in the States.