Have you tried talking to Terry Foxen at
GEE? If he hasn't got one, there's always the option of getting a local engineering company to re-make the worn bits.
There's a small engineering outfit run by some pals of mine in the same building as Terry that quite often make parts for him. You could probably find somewhere close to you that could do the same.
If it were me, I would take the steering box and go to your local industrial estate and start asking around for small engineering companies that do one-off jobs. If Germany is anything like the UK you'll find plenty of them in every town. Somebody will have look at the box, figure out what needs doing, and if it's not something they can do they will recommend someone that will be able to help.
In my experience I have found that they all know each other, they each have their own specialist skills, and they work together in an informal network to get jobs done. The more interesting or different the job is, the more helpful they are.
