I _must_ clean mine before my next printing session.
I see dust on my neg, so I clean it carefully by inspection, I put it back in the enlarger and the next print has new dust on it. It must be picking it up int the enlarger so I'm going to make it a project to clean the condensors, blow out the bellows and wipe down all the interior surfaces.
Hopefully, I will get the time back in reduced spotting time.