jetlude

I have been using Castrol full syntec oil for my boosted lude for some time now
I pulled my hood this morining and noticed some oil spilt in my timing belt area. it seems to have come from my dipstick port. I immdiately used a strong detergent in water to clean it up as best as I could, now I dont see any trace of oil left on it .

Question... is full synthetic oil as dangerous as petrolium oil on rubber. Should I change the belt??