A couple months back I bought 2003 Jeep Liberty Sport 4x4, 3.7L engine, automatic transmission, and only 104,000 miles for dirt cheap! The owner swore up and down that it had a bad head gasket and that was all that was wrong. I did test drive it and figure out really quick that it was a broken valve cover gasket, not the head. Had that confirmed by 3 separate mechanics, fixed it myself, along with spark plugs, oil change, and 2 vacuum hoses he "fixed" with tape. Since then, I've discovered a few more of his "fixes" on things I'm planning on doing anyways, first one being replacing the upper and lower radiator hoses because I found the lower hose wrapped with tape under the clamp, thermostat, water pump with a new belt and a coolant flush, and the other fix is partially my fault, I read the oil cap, not the book. I discovered the oil cap had been replaced with one that says 5W-20, not 5W-30 like the owner's book and parts stores recommend. I plan to use 5W-30 full synthetic, but do I have anything to worry about from using the wrong oil? Is there anything else I should check and/or replace? I'm eventually going to replace all the exterior lights and back door and glass because previous owner used the spare tire as a stopper and the door is dented, and the glass is only holding on to a third of the latch. Thanks a bunch!