[Aussie Mike]

Its a pity you don't live closer Ben.

You could try dot punching around the pin hole to see if you can move enough metal to close up the pinhole.

I'm not so keen on using a putty to repair as when it comes to welding it up properly you will need to grind all of it out.

I've had some success with Devcon. Its a metalized 2 part putty and it sets rpck hard. You can machine it once its gone off.

If you do pull the rad bring it over and I'll weld it for you.

Cheers