Sounds like the T-400 forward clutch is a problem.
Was the T-400 parts replacement job performed with a full paper and rubber kit? Sealing rings in this T-400 were metal or a teflon looking material?
Clearances on the clutch pack of this T-400 were set at what clearance?
What condition was the pump in this T-400 ? Was the side clearances of the gears checked in this T-400?
Dont worry how old you are... it is the mileage on your body that adds up.