In the late 70s I had a Morris Marina on which rust would eat the cills for fun. Lower down from the pic the cill design is exactly the same for the MG4 where all the metal parts join in a vertical seam which is spot welded (burns through the protective coating ) and then painted body colour. It's directly in firing line from crud from the front wheel which could be salt, chippings, general road muck. It might not be a problem for a few years, but I think this is going to a future weak point for owners who intend to keep their cars for a long time. Back in the 70s there was a government pamphlet, Protect and Survive, wasn't really about Marinas, but I should have took the hint and gave it some extra paint / underseal which is what I've done with the MG4, I've also put it under a large table, just in case!