I have read it is very common. It was something I found out about after I bought my JK and was doing searches to find out issues and problems. This is something I should have done before I bought the vehicle but I have not developed oil use, manifold cracking, or the hot oil message for the transmission. I have, however, had the broken transfer case clip (under the console), hood lift issues (not fixed with spring removal but now cured with Drake pins), and poor fuel economy. All in all, my JK is a good vehicle that has a high cost associated with it for fuel, but is very cheap to insure so that actual cash flow of monthly ownership is lower or very close to other vehicles that get much better fuel economy.