Hi craigb
I think the small screws could be BA, I have a spare set somewhere, they have a rounded head with screwdriver slot so don't impress on the rubbers
mostly the rubbers themselves are just not the right quality and the split I doubt is to facilitate fitting, more likely just poor rubber.
Mine went on then after a short while they sort of ripple, so leaving gaps along the top and bottom edges.
I did purchase some a while ago advertised as made in England, haven't tried them yet, but will be pleasantly surprised if they are good as hey used to be