Have you figured out where it leaks? A thorough cleaning may help if there's a film of gunk stopping the glass from contacting the rubber.
You might manage to pull the glass closer to the rubber by adding some packing under the catch & hinges.
There are various rubber mouldings that might be worth a look to supplement or replace what's already there
The catch doesn't seem to pull it down enough so there's a gap around the back. Packing it looks like it'd close more, not less, due to the design of the hinge.
Sometimes taking the rubbers off and swelling them can fix the leaks.
Making them slightly thicker and sealing better.
I've taken the rubber off reseated it, it does seem kinda squished even when you take it off. What would swell it?
Your best bet is to visit a sunroof specialist and establish whether the seals are still available. Mine on the Midas was a 1981 sunroof, and therefore there was no longer anything they could get to fit.
Then it's up to whether to get a new one fitted, or bite the bullet and do either a Webasto conversion or have a new roof skin spot welded on.
Tried Bristol Sunroofs online, they said they don't have parts for this one. Emailed Somerford to ask if the seal they sell for the RSP one will fit this, not replied yet.