Is the fan original? If not, it's a neat job. If not, I wonder why it needs one... An image search fails to show up one with a similar fan, so perhaps it is a mod.
It's compos mentis which is a start. Just dirt, loads of dirt. I did wonder about the grill on the top as well, suspect it's been modded for warm climates and has found its way back.
Ah - so just a grille, then. That's good - nothing worse than fan noise, especially from fans of that era
I guess that finding a replacement top panel might not be impossible if originality is important... Ventilation is good, but on the other hand, my cellar workshop is rather dusty...