Maratac AAA low output.

Hi
I've had this copper aaa for over ten years.
At some point it's output got either stuck in the low mode or there's something else limiting the output.
It's been in a draw for a few years but I thought I'd see if I can fix it today. So I've dismantled it and used acid to remove any oxide from the copper contact points and contact cleaner everywhere else. I'm happy the internals are nice and clean but that didn't fix the output issue so I guess it's an electronics issue with the module.
I was wondering if anyone could suggest anything else I could try to get it going again?
It served me well for many years of crawling around dark floor and ceiling cavities and cable risers.
It would be great to get it going again.