discovery td5 top windscreen finisher wont stay in place! please help

Hi all,

the top windscreen finisher on my 2000 td5 came out one day on the motorway, and was damaged in the wind.
i have bought a new one, but it simply wont stay in place, it fits perfectly, but is loose, and will certainly come out if i drive at any speed.
does anyone know how this is supposed to be kept in place?
there doesnt appear to have been any fittings on the old one, and nor was it sealed in place.
it seems that it is supposed to "clip" between the roof and the glass, but it appears that the gap is slightly too big, how could this be, when the original one was in there for 11 years with no problems, why would it suddenly come out?
and the new one is exactly the same size as the old one.
any help would be greatly appreciated

cheers

Often just an interference fit.

If the edge of the roof rusts which is common for all discos, then the seal can be pressed away.

It's nothing a healthy application of sikaflex can't sort out