Please can anyone offer me any advice regards water in me boot?

This concerns a 1985 Mini City E.
Original boot seal fits to the boot lid with clips. This seal was k-nackered! It has proved impossible to replace, at the moment. I did buy a boot seal to refit using clips, but once this was in position, it was totally impossible to close the boot lid. I sought advice from the seller of the boot seal, & was told that I would need to force the boot lid shut at first, failing that, I could fit a boot seal to the body of the car...
So! Even with myself & my fella together applying pressure to the boot lid, it would not come close to shutting... At the moment, I have fitted a car body seal, I did have to apply a little force to the boot lid, but it has shut tight. However, I do not seem to have cured my leak & the car boot is still getting wet!!!
Help please!

1. Where else could water be getting into the boot? I have tried pouring water around, but as I cannot sit in the boot with it closed, I can't pinpoint the leak in, at the moment.
2. Would I be better off hunting down the boot lid seal for this car? I have seen a "genuine" one available to order, at the cost of £40...is it worth spending this? is it more likely to fit properly?
3. Should I just emigrate to dryer climes...?

As always, all advice is very gratefully received!
Mini regards, Rosie.