The problem Paul, was the balance shaft keyway was often not centred accurately; also by design it was very loose, to prevent a twisting torque snap, that would never happen, and with 77mm the hex key was only into the keyway for about 12mm. So for some if not all (they all will fail at some point no matter) even the most diligent and regular OCIs could not prevent the inevitable. I don't think it was calculated obsolecence or even penny pinching, I think it was more German hubris in engineering (software material design engineering rather than actual physical testing) that exist more and more even today - wetbelts for example.
The later B8 2.0 tdis (late to post 2010-15) with the 100mm hex key are not immune either. All they did was extend the keyway but leaving the first 20 or so mm, I can't remember how much completely loose, so that you got 23mm in the balance shaft rather than 12mm in the same sloppy keyway (you can see some denial and hubris again in that engineering revision). Graham from KMB says many of those have failed too. The only and permanent solution is such as KMB's which is a hardened chrome vanadium insert, properly centred and much tighter fit, right from the edge, so using something like 35mm of the revised solid 100mm hex key, to much closer tolerances than Audi/VAG themselves.
I should add, as I said before, good regular OCIs of 6K or thereabouts, will delay the inevitable, it was just with yours it was most likely one of those improperly centred, mine was most likely and accidentally better centred - the tip edges of the hex key only just touch the loose journal on the balance shaft (and oil pump), so any slight off centreing will greatly speed up wear too. It's a gamble in the end not worth taking. I was in an Uber the other day (a Goddamned Tesla Y - horrible car but that's another story) and the driver had one of these PD 140s in a Passat that finally went at 350K - they got very regular servicing and were warm all day, hence the longevity there.
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