Slider potentiometer changeover

Hello.
While I was driving on the highway today, my Audi B4 TDI 1Z, manufactured in July 1992, started to jerk intermittently. After hitting a large bump, the control lamp on the engine control unit also came on. Reading the error memory resulted in the error code "00541 Potentiometer for slider position (G99); 27-10- implausible signal - intermittent."
To the best of my knowledge, that's the feedback from the actual injection amount. Or is it?? My repair manual only says "have it replaced ". Can't I do that myself?? I've already done quite a bit myself (like replacing the head gasket, etc.), but I don't really want to disassemble the fuel injection pump. However, I haven't checked the plugs and wires yet.
Is the replacement difficult, and what is the cost of a new donor? Or can I not do it myself?
Thank you very much, Wolfi.

Regarding the "successor" device, the HDK sensor in the quantity setting unit, I know that not even all VW or BOSCH workshops are able to handle it, and very few actually do.

Most of the time, the entire pump is replaced.

But first, check the plugs and cables, maybe there's just a loose connection.

m;