Thanks for all the replies. Jack, I doubt if a soft hammer will do the trick, as there is nothing for them to seat on to and not enough meat on the caps. The caps fit over the nut okay, but there is no space left in the cap for it to physically go any further without breaking. I think Paul has hit the target dead centre. The Rover wheel sets are being sold on ebay and my guess is they are coming from China, or are being put together in Australia using Chinese stock from various sources. So they are not really O.E.M. ("aftermarket"). They are more like "long time after-the-fact aftermarket". LOL!
I could have bought original caps when I purchased the wheels, but I told the seller I did not require the caps. DOH! I was depending on the aftermarket ones being the real deal. Obviously they are not!
Anyway I will use a small spot of silicon gel behind each one, which should do the trick. I can always remove them in future without causing any damage.
