The Raffin service department is extremely helpful in such cases;
unfortunately I guess long distance telephone charges to Germany might
apply, also the language barrier...

Personally I would use "Holzleim" (standard household wood glue):

- fit the pipe in;
- over the thumb determine where the "edge" on the tapered part would be;
- apply a ring of wood glue just below that line;
- press pipe back in (the glue then will spread to the right position);
- take piece of cloth to wipe excess glue and build a nice "ring" that way.

Cheers
Ingmar Krause
Burnaby, BC, Canada