I have a 2002 Jetta 1.8T with about 78K miles; have owned it for the last 50K miles. A friend of mine told me I should switch to synthetic oil. I don't know if I have a sludge problem or not. So -- what are the potential problems if I switch to a synthetic oil now? Do I need to run some sort of cleaner through the engine first or with the first few synthetic oil changes? Or at this point do I just stick with the regular oil and hope for the best? I do not change my own oil; I was taking it to the dealer but have now moved to one of the quick oil change places.