Curing O.D.S. (Oily Diaphragm Syndrome)
This is my experience too. Once the oil begins separating from the thickener, it will continue to weep oil until its gone. Some unscrupulous shops only clean the diaphragm, leaving the old, deteriorated grease in place.
I think that this is likely due to overheating of the lens at some point. Possibly it was left in a hot automobile in the summer.
It might take a year or longer, but eventually more oil weeps out and once again fouls the blades.
Only by removing the old grease and replacing it with fresh grease of the correct type can ODS be stopped.