[Land-speed] Vegetable spray removal?

[David Dymaxion]

We had heard that spraying vegetable oil on the underside of our car and truck 
helped limit the amount of salt that would accumulate. This worked great. This 
year my wife ambitiously also sprayed the paint of our car and truck. It worked 
great, the salt didn't stick. The only problem is, many car washes later, it's 
still there. It took a plastic scouring pad to get it off the windows and metal 
bumper -- I'm afraid to apply such harsh treatment to the paint. What would 
those-who've-gone-before recommend for removing the vegetable oil but not 
hurting the finish? Many thanks.