For Kugelfischer XN2 injection system: New membranes (can easily be mailed to you).
Does your 2.0 liter 504 injection engine start consuming more and more gasoline and you can't figure out why? Then there is a fair chance that the membranes that control the vacuum inside the injection pump got porous. This is especially very likely when the car wasn't used for a year or two. Problem for most of us is how to get those damn membranes. I know of stories where injection engines were being converted to carburetor engines just because the Peugeot garage, those Peugeot 504 owners had a good relationship with, knew everything about their 'baby', except where to get spare parts for the injection pump! I do sell new sets of membranes, including instructions for replacing. If you find yourself in a similar situation, just send me an email (at joost-AT-wisint.org) and I get you a new set as soon as possible.