I need to do a little work on my Jeep 4 liter engine, it has 98,000 miles on it, but I will be replacing most of the seals so I'm not worried much about it starting to leak from somewhere. What exactly are all the benefits of synthetic oil? Are there any disadvantages? I still would probably never go more than 5k on an oil change...even though my manual recomments 7500 on dino oil...