The repair uses a bought in centre cap, as the old design used material that wasn't flexible enough, and then a specially machined insert to hold the cap in place.
Here are some pictures which will explain it better.
Old tabs are machined off to keep a nice flat surface and a new cap glued and bolted in place for added security. Under the Hartge sticker the cap is hollow so a counter sunk bolt will fit with minimal modification.
An insert is turned up to sit inside the old clip groove and is gapped like a piston ring to fit tight in the bore.
Fitted, nice and central just like and original.
They fit with a very reassuring clunk as they lock in.
I would need to have your centre cap to put it in the lathe to make sure the hole and clip are fitted centrally and then post the cap back with the insert.
If you are interested post up how many you would be interested in, once I get an idea I of interest i can get some firm prices and go from there.
Also if you have any spare caps with missing clips you don't want anymore i'm after two my self so PM me as i would be interested in buying them.
Thanks Matt
