Ford Powershift Gearbox problems & solution

Описание: Symptom: Engine speed oscillates when going at constant speed up a steep hill, (or a gently incline when towing a caravan). Sounds like a clutch slipping, then engaging, then slipping. In this video the vehicle speed was held constant by using cruise control, but the same happened under foot control. Symptoms are more severe when towing a caravan.
Apparent reason: The dealer failed to do a gearbox/clutch oil and filter change at the 37,500 mile service. Changing oil and filter has stopped the problem. Thus it seems that a combination of clogged filter and reduction of viscosity of the old oil was sufficient to lower the oil pressure used to engage the clutch. This allowed slippage. As engine speed (hence pump speed) increased, oil pressure increased sufficient to stop the slippage. As engine speed reduced, oil pressure reduced, slippage occurred again, so continuing the cycle.
Big question, how much wear and damage has been done to the clutch in the 10,000 miles it took to identify and rectify the problem?
I hope this information helps anyone out there with the same problem.