I'm changing my oil tomorrow and switching to a full synthetic (mobil 1) and its usually a pain to do it myself with out a lift....so i went to my friend who works at a monroe muffler to see if i could use one of his lifts...anyways when i told him that i was switching to synthetic he first asked me how many miles i had on my X ('02 with 22,000)...he said that with higher miles when a car is run on regular oil and switch to a syn, that the seals and rings or something tend to dry or crack which may cause leaking, but around 30,000 to 40,000 mile is where you should be carefull with the switch...is there any truth to this...he also said that if you use a blend for a while and then go to a full syn that this can help..any comments?..thanks