I had the same problem appear on Saturday - and the old grey matter fired up and reckoned there may be an oil cooler in there... Only just bough the car so getting to know my way 'round it, can even open the fuel filler cap now.
There are loads of posts on this site about this issue. There is an oil cooler in there, plus two hoses - it seems to be the unions on the hoses that corrode and then leak, if they're not sorted out properly the corrosion can also affect the oil cooler rad.
Irritatingly, ( I've just bought mine with fsh ) the main dealer that serviced the car on 9th March this year, less than 2,000 miles ago, didn't spot the problem! That was on their 'Gold' service package - luckily the bloke I bought it off didn't go for the Bronze
I have just 'spoken' with said dealer, who was 'disappointed' they didn't pick it up... Definitely worth adding to the list of stuff to have a look at when buying a GT - seems to be really common.
Just been to Gonellas in Catford, it is a corroded pipe; booked in to change the offending hose on Wednesday.