When I got my Favorit a while back the wheel well was full of water, and the boot rather damp. On drying the boot out and removing the carpet shelf and rear seats, pouring a bucket of water over the top and going via rear doors to check for leaks it appeared to come in between the seal and tailgate at the bottom, so I stuck a strip of bath sealant stuff to the tailgate at the point which met the seal. I also sprayed silicone oil onto the seal. This seemed to stop leaks in all but the heaviest downpours and when heaps of snow was left on it to slowly melt and drip in.

I've just been to the scrappy today and got myself a tailgate seal off a felicia for £4. Other than needing shortening by an inch or two it's a perfect fit. Also, the boot would not shut even with my 20 stone weight bearing down on it until I removed my earlier sealant strip bodge-up. The boot is still more difficult to shut than before (and I have ensured the seal is correcly seated all the way around). Guess that shows how much the old seal had worn. Luckily the silicone oil/grease trick still seems to be enough to stop the drips from the sunroof.

There is also signs of water in the rear lights so not sure if water is getting through there somewhere too or if it's condensation.

Currently drying out the boot and carpet and awaiting a heavy downpour to see if any more gets in (now I want it to rain it probably won't, lol). Will report back

You might find you can get the sunroof seals relatively cheaply and the rear light clusters will have a rubber or foam gasket on them

If you can't get the OEM seal for the lights, then try a suitable stick on draught excluding P ot E gasket that can be purchased to stick on window frames etc.

Also, most of these seals are one of relatively few sections, so a "practical classics" type mag is likely to have an advert for a place that sells the right section for any given application by lengths.