So close.....
Best guess the intercooler caught a rock awhile ago and all the recycled exhaust soot has built up and slowly forced the core open.
Had the "it's making a funny noise" phone call from Mrs George on Thursday night. Brought to where I was working and I thought it had split a hose. But no, it broke the expensive bit.
Thankfully it's a manual coz the trans cooler would've been right in the way. And also thankful it was the intercooler, not the radiator. I can handle it running a bit rich from a leaky intercooler, the computer adjusts the fueling anyway. Don't really fancy a cooked engine block.
Bush fix closed the hole up and now the check engine light has gone off