With a little patience and a good flashlight you might be able to see the source of the leak from below without removing anything. Of course with such a low car, you would need to jack up the front end and use jackstands for safety. You may need other parts as I mentioned earlier.
Perhaps the garage should get it onto a lift, remove the bumper skin and get a good look at it before ordering parts. The car can be driven into a yard for storage for a few days without the skin.
There's good slide show instructions somewhere on this forum if you need them.

The radiator was out yesterday evening. No obvious cracks or damage to the exterior.

Just the bottom corner which was yellow from the coolant and appeared rotten. The metal honeycomb crumbled when touched in this area.

So remains a bit of a mystery..photo attached. New radiator now in place. Cost £125 OEM.

Attachment 16773

No mystery.....Your radiator was ready to start leaking and you footballed it over the edge. You never mentioned the yr of the car or the miles on it. Do you KNOW about the coolant that was in it? If some replacement coolant not designed for the car, it could lead to early rot. Also, organic debris stuck in the radiator could possibly rot it from the outside. I hope the mechanic checked that out on the opposite side while the bumper skin was off. You got away easy....could have been worse.
What kind of coolant was installed with the repair???????

Thanks for your comments

year 2003 - 93k miles.

There was plenty of damp rotting vegetation in the leaking radiator.

Mechanic charged 3 hours labour. He did clean out the other radiator while the front skin was off.

The coolant previously in the car was yellow.

The coolant now used is a Pink colour - apparently its the most expensive stuff.

Im looking to change the car but cant really decide what to go to. The Cayman is nice, but more costly for essentially the same car. A newer Boxster is kind of the same again, and an Aston Martin v8 Vantage is 30k! plus running the thing.

http://986forum.com/forums/uploads01...1356279336.jpg
I had a self imposed hole in my front radiator from drilling a hole to run a wire. I will explain how I fixed it.

Revove the front bumper. There is a good post on this forum about how to do it. There are then two hoses and 4 bolts to remove the front radiator.

Once removed, spray the area to be patched with brake cleaner. Picture Shown. The guy at the autostore said it romoves the oily residue from the coolant. Then mix the two part epoxy and push it into the radiator as shown.

http://986forum.com/forums/uploads01...1356279603.jpg

http://986forum.com/forums/uploads01...1356279685.jpg

Leaking Radiator
 

I was able to see if the epoxy stopped the leak by plugging the inlets with wine corks and submerging it in my sing.

If the leak still exists, you may have to do the following.

Remove the end cap on the radiator by bending back the tabs holding the plastic end. The end cap will come off. You will need to idenify which port the hole is in. Lucky me it was right on the end of one of the ports. Otherwise I would have to plug multiple ones.
http://986forum.com/forums/uploads01...1356280101.jpg
Drain it, and spray the areas with brake cleaner. mix the epoxy and push the epoxy in the port of the one with the leak. Let it dry overnight.

http://986forum.com/forums/uploads01...1356280228.jpg
If your hole is in the middle of the port you will need to plug both ends.
Test it in the sink.
This is about a 2 hour job.