Now dont get me wrong, sicaflex make some spactacular products, and I have used a few different ones.
But I do not believe that it will produce a long term "as good as welded join" in rubber like a good quality cyanoacrilate (superglue ) will.
Good superglue works incredibly well on tight fitting rubber joints.
Done properly and you will not seperate the joint at the glue line, chunks will tear out of one or other part of the joint.
A large proportion of commercial refigeration seals are done this way and most of them fail elswhere than the glueline.
Water and UV exposure are less of a problem because of appart from the glue being very resistant the glueline is soo thin there is almost nothing to expose to the eliments.
Those made to length "O" rings are joined with superglue and they will (if properly done) withstand all sorts including being used as drive belts.
Do the joint properly with a good quality superglue and it will be durable and permanent.....and with some patience and skill... very neat.....
cheers