It's a #2 Lanchester balancer shaft out of a VAG 2.0 TDI .
The original 6 x 77mm drive key has an oil pump cassette the other end that's retained by a circlip .
Oil pump drive is lost through the balancer shaft keyway wearing as it is not deep enough , hard enough and isn't even hexagonal but a 15mm deep bore with 6 tiny machined grooves to accept the very tips of the hex key .
The hex key also wears and if just 0.5mm is lost then it rounds and spins , oil pump drive is gone .
Compounded by a stupid low oil pressure warning that only operates above 2,000 rpm.
In the early days before the discovery this could see people fitting new oil pressure sensors and having it idle for many minutes all the time with no oil flow .
VAG did improve the design with a longer 100mm key and deeper balancer shaft keyway that then provided 35mm contact length as can be seen when withdrawn and a smaller amount of wear is observed .
The bullet proof remanufactured modified kit is the 100mm key but the balancer shaft receives a deeper keyway by it not being recessed at it's beginning and harder materials and actually hexagonal !
This sees a 38-40mm contact length and now surface area contact .
In Poland their solution is to oversize both the key and keyway .
But you'll still get confusion about it as some think that just a renewed 77mm key will surfice or they can fit the longer 100mm key which would be impossible .