1098 radiator leak
Mine did this at the end of last year and faced with the options of replace at silly money or re-core at half the silly money I took the advice Kempston Radiators in Bedford and allowed them to seal the top tube on the core which is the one that always splits.
There should, according to them, be no further leaks - they've done a few of these over the years and have never seen one come back - and it cost less than 60 quid all in including a re-spray to make it look smart again.
This will, of course, have reduced the cooling capacity of the rad, but the argument was that this wouldn't really matter much at speed, and when stuck in stationary traffic the top tube is not covered by the fans so shouldn't make a huge difference at the point where the bike is likely to get hottest.
We'll see how things go as the weather warms up...