I bought in german ebay a four jaws independent chuck with DIN 55022 number 4 fitting. This was not the kind of independent chuck I prefer for the Leinen lathe. I would prefered those kind of “old” chucks which are lighter than the modern ones. Having found no provider for these lighter chucks, finally I went for this one.
The chuck can be seen in this picture:
The chuck was in pretty good condition. However, one of the jaw guides was notoriously worn. My father proceed to mill the chuck guide using a t-slot cutter, then adjusting a steel part to the milled slot, and finally glue it and mechanize the new guide. The repair was a success and the jaw is tightly adjusted again. In the picture below you can see the traces of the rebuilt guide. Look at the downside of the jaw chuck guide :-).
This is the chuck fitted to the lathe nose: