The roof of our Daimler is made of a "leatherette" material, with a canvas backing. It is basically made in two pieces and stretched over a wooden frame. One piece forms the top, the second wraps around the sides and rear, with expertly-made darts to give a rounded exterior. It had suffered in the fire which destroyed the previous owner's garage, but had been repaired with a flexible sealant. However, once the car was out in the open and exposed to real weather, one of the seams tore open.
A more permanent solution was needed. Replacing the roof would be out of the question. Are there still people capable of making such a roof any more? If so I expect the cost would be huge.
After much thought we came up with a low-tech solution - a patch.
We got a sheet of the thinnest plywood we could, and covered it with the modern equivalent of leatherette.
The edge of the top panel was cut back so that the parts would lie flat:
Plenty of masking tape ensured that things would line up properly, and the sealant we were about to use would not spread too far. Here's the patch panel in position. The reason for its large size lies in the wooden framework underneath, We needed somewhere solid to fix it to. There are thin supports across the roof, but substantial ones at the rear and the centre which would be a sensible place to put woodscrews.
Sealant was applied under the edges of the patch, then aluminium moulding was screwed down to hold the patch in place. This too was bedded on sealant.
The end result is quite neat. In addition, few people see it. After all the top of the roof is all of six feet above ground level.