Just bought a 72 AMC Jeep J2000 4x4 with a 360 and a TH400 transmission. It hadn't run in over 15 yrs according to the previous owner. Got the engine to run but the transmission will only run rough for a few minutes then it will not go into any gear. No forward, no reverse. Once it cools down for a bit it will engage for a minute or so then back to not engaging. Plenty of oil, red and clean, does not smell burnt at all. Any advise would be appreciated. Thanks.