I once spent a fortune with so called specialists repairing my boat canopy and in the end made a much stronger complete one using lorry curtainside material and an industrial sewing machine, though as it was from scratch I was able to use a powerful heat gun and a roller for the seams, which is what the lorry companies do but me liking belt and braces went over it again using industrial thread and the big sewing machine.
Obviously with a classic you will probably have to find a specialist and hope they make a good job.
Sometimes a good industrial seamstress/dress maker can take on work like that, you may have to strip it off for her to do it, mind you to keep the price sensible that may be necessary for the specialist. The other thing you may find is once it comes off, it can be hard to stretch it back into place.
Cheap option duct tape????


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