In my experience, the early HP22 tranny (4 speed overdrive w/ lockup, no electronic sport/economy selector) will last indefinately if the oil filter is changed yearly. The weak spot on these units is the clutch pack seals. They start to leak. If you rev the tranny in N or P, the leakage will pressurize the clutch pack and burn it out. Don't rev in N or P and you'll be fine for a long time.