Parents Sky dish had never been touched since installation and all fixings were secure. So either 5 satellites have moved without anyone noticing, or Sky installers are not to be trusted. I know which one my money's on!!
You might consider replacing the Co-ax if it's the cheap (and nasty) aluminium foil screened variety. Decent CT100 should have both a copper core, and copper braid & foil screen. This also greatly reduces the risk of corrosion through dissimilar metals in contact with each other. Do make sure you seal the cable connection with some self amalgamating tape stretched tightly, and overlapped 50%. Hopefully Screwfix will be able to sell you some.