After some prodding by Ken and Stuart I've decided to attempt reforming caps. This caps in question are NOS from the previous lucky dip video.
Here are some links I found useful. However, in the first link the author says to apply full the voltage rating directly to the cap. I would not do this!!!
Start off at low voltage and build up the power in increments, finally reaching the cap's rated voltage.
https://www.6v6.co.uk/vcomp/tech_tips/reform_caps.htm
https://www.casa.co.nz/capacitors/electro/CAPACITOR%20REFORMING.htm
