Tony wrote:

I have read up all I could about it (including all of Nina's old
posts) and
there seems to be little I can do to erradicate them.

I don't need to say much, then (lucky for everybody). Yet I must
repeat, as I have 10,000 times, that borers are a sign of stress, and
in your case, the stress is tropical conditions on a boreal species.
Next time it might be a botryosphaeria canker... there are lots of
organisms that will attack a stressed tree, but not a healthy tree.

That being said, if you don't mind dead-wood, you can carve out borers.
I had an apricot bonsai that got plum borer (a borer that can only
penetrate at a pruning wound, so can be prevented once you know what's
going on). I successfully eradicated the borers and the tree thrived,
but the surgery I did looked ridiculous on a non-conifer, so I gave up
and planted the tree. As soon as I find a good source of single-white
blossom flowering apricots, I'll try again, because I love apricot
flowers. There's something so pretty about such delicate, fragrant
flowers blooming so early against a background of black bark.

Nina