Jack Jones wrote:

Now I need to do some soldering again. Would that old 60/40 multicore
of mine have deteriorated?

Sad to say it has definitely gone off. Safe disposal will be costly so
please pack it carefully and send it to me QTHR where I will dispose of
it at no cost to you (probably on ebay).

I have solder well over 20 years old that is still fine to use...

--
Visit the Amazing Online Fleamarket at http://www.fleamarket.org.uk

Always lots of amateur radio gear!