It’s not so much the coolants fault: it’s lack of regular maintenance.
If I may reanimate this thread, which shows that I actually use the search function 
I am now working on my 5th XK engine and been watching at car shows many engines who sweat under the acorn nuts.
In my eyes, this is a poor design. The water creeps up along the head stud and seeps out between washer(s) and head or washer and acorn nut.
I took off one nut at a time:
I smeared sealer onto the first protruding thread and cylinder head washer/nut surface (where the washer rests).
I also added o-rings into the sealer. This O-Ring is now held (surrounded) by a metric 12 mm washer and on top of that I place the original 7/16"x1" washer. Now the O-Ring is trapped, but not squished when I torque the nut.
The 12 mm washer and O-Ring kind of resemble a Dowty washer, seen at sump plugs. But the ones I could buy were just too big in ID. And too small in OD.
It works.
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Just add a tablespoon of ground pepper to the coolant.
Catapillar mechanics do it every head gasket.
Look at Alumiseal now.
Its over priced ground pepper.
When it gets wet, then hits air it expands.
I have been using it for 50 years.
It sounds crazy, but it works.
Your in-situ solution seems a good idea.
My preventive solution was to put a fillet of silicone sealant at the base of each head stud, at the block deck, such that when the head clamped down, it formed a seal between the cooling passage, stud, and the head.
Never had a leak.
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