[ian1959]

An oil sample would have shown the pump spline debris in the oil, mine did! it was like very very fine dust, and just like yours the splines were almost gone on the V20 Vickers pump, your drive splines will be worn, not as much but they will be as the Cat gear is harder material , if you look at the housing that the drive gear is in it is lubricated by the engine oil and there is a small cut out at the bottom of the housing to allow the oil to drain back into the timing gear cover, this oil along with the worn spline metal goes into the sump then out into the engine, the filter will not get it all, I always cut open my filters, I was horrified when I first did mine, it was full of bronze bearing material which I found was the thrust side of the crank thrust bearings, which is the front one on a C15 with the AStronic gearbox as it is a pull type clutch cover and not a push type, the clutch actuator was faulty and always had preload on the clutch which wore out the trust bearing.
The Cat part number for the drive gear is 6I 4575, and the Vickers input shaft is the 11 spline type, 180.00 Euro plus tax.