My F-150 Ford Truck (1998 Model) lost compression, idled rough intermittently, jerked vigorously especially when on reverse and soaked plugs with oil. It took my mechanic 3 hours to painstakingly bring down the very massive gearbox to replace the clutch plate. Now, the gear makes a loud noise and won’t engage after dismantling and reassembling over and over. What should we do for the gears to engage smoothly before we attend to the other problems?