Coolant disappearing

I had my low coolant alarm sound on startup and found a dropped level in the expansion tank. I topped up and suspected a failed expansion cap so I changed it.
Shortly afterwards the low alarm went off again.  Switched off.
Checked the level and I could see it dropping as I watched it.
Checking the car, I could see wisps of steam from the radiator area and coolant dripping from the offside.

Whipped the slam panel off and saw this.

 

Can you see the problem?

No, how about now?

 

That'll be a new radiator required then.   So relieved this happened on my drive,  not on the motorway at 70mph. 

Strange fail, I have never seen this on a radiator.

Is the end cap plastic or metal?

The end caps are plastic. I've ordered an all aluminium replacement.
I agree it's a bizarre failure. I can't understand why it would fail like that, but hey ho...

Hi David, You're right, glad it happened on the drive, not the motorway. And true, odd failure point.

Wow , never seen that sort of thing before . It must be catching as my TF is in a lock up away from my abode and I thought I'd just have look to remind me of what it looks like . Lifted the garage door to find a large damp patch on the floor of the garage  . Dipped a finger in and tasted it and yep that's coolant alright and it's from the the front of the car . Must be the time of the month !       

John .