Many thanks for your help - that fixed the problem.
I never, never, never would have got the idea of changing the mirrors, because all other updates were 100% present.
After changing to packages.siduction.org I got much more kernels - but neither upgrade nor full-upgrade have got any new package that was not already present at the "spline" - mirrors.
This is very, very strange...
Best regards
DF 8 OE