Windshield Fluid is very oily again! Nissan Altima

Hello All,
The windshield fluid for my 2012 Altima has oil in it again! when I ran the windshield wipers this morning the windshield cleaning fluid came out milky and oily! thus, it left a thin film of oil on the windshield and make the windshield look dirty and very cloudy! This has happened 3 months ago. last time it happended, I ran the windshield container fluid empty and clean it very good before I put the windshield fluid back in. it then stop the oil fluid but until now it comes back!
I am dumbfounded. I only go to the same Nissan service facility. I can't imagine that it is possible for some kind of oil leak into the windshield wiper container!
I am taking the car to Nissan service on Wed. and see what or if they can find out how it happens!
I just wonder if anyone experienced such an issue for Altima Windshield fluids!
Thanks,
Astroboy.