"Doki" gurgled happily, sounding much like they were
saying:

But, as Dave P said, most leaks are down to blocked drain pipes. The
seals are never perfect.

Sunroof seals (assuming it's a factory-fit-style slider/tilt-and-slide
rather than an aftermarket-style pop-up) aren't designed to be
waterproof. Merely water-resistant. The drains SHOULD take any water that
gets into the tray away.

Shagged or missing seals should just result in a bit more wind noise.

Open the roof fully and in each corner of the tray (the rears may well be
very hidden) will be a drain. Something stiff-but-flexible should be good
to give them a quick dyno-rod without dislodging them. But be prepared to
drop the headlining...

Or, considering it's a near-decade-old Rover 25, just get the gaffer tape
out. If you do use silicone, make sure it's not the acidic-cure type,
else you'll have a far bigger problem.