Most used car lots will steam-clean the engines before putting them up for sale, but private-party sales are normally sold in as-run condition. It’s not uncommon for the plastic valve covers to pooch out a little oil from time to time. Don’t confuse this with leaky head gaskets. On the automatic transmissions, pull the dipstick to inspect the ATF for a burnt color or smell. Early auto-equipped Wranglers lacked a tranny temp gauge or even transmission idiot light to warn of high transmission fluid temperatures.