Cheers Al - certainly looks better without broken images.
I think another dozen would clear up the entry-point pages like:
/users
/top
/new
/categories
Obviously, neither urgent nor important!
Edit: I notice the replacement URLs are not visible in my post above. Let's try this:
https://forum.mystorm.uk/letter_avatar_proxy/v2/letter/r/a4c791/120.png
can be replaced by an upload from
https://avatars.discourse-cdn.com/v4/letter/r/a4c791/120.png