Yeah, I was finally looking at it critically, with my glasses on (what a revelation!) and the right place to cut just presented itself very clearly.
I'm thinking I'll keep the two of them out of the sun for a few days to let them recover from surgery. Will update with any surprises. (hope not, surprises could only be bad, I think)
This week I am due to treat with fungicide again, also. That will ease my mind about fungus invasion into the cut, too.
