I decided to do an update for anyone interested.
Basically, I 'bit the bullet' and removed the head. I think the K-seal/ Steelseal etc would have fixed the problem, at least temporarily but as it's my partner's car and we wish to keep it a couple more years, I thought a proper repair would be appropriate.
First off, this is a big job in the Mini. So much needs to be removed before you even have chance to get at half of the fixings. I'm sure a pro in a warm, well equipped workshop can bash this job out in no time! But for me, working alone in a crappy single garage 30 miles from home (and my tools); I found the dismantling very time consuming.
As it looks currently...