Hi Dave,
Greetings from a Brit in Belgium!
Thanks for this - I have been a long time silent viewer and learnt many things from you which bravely made me fix my mums electric shower and a whole host of other stuff. I recently got the Hakko FX-888D on your recommendation and am very happy with it. Gush over!
I found this vid really interesting because I am a bit of a computer geek, amateur composer and owner of a pair of KRK Rockit GII 5's for 7 years.
I've not had a problem in all that time (well, I did get a nasty hum once, but it turned out to be a dodgy power pack delivered with a Korean monitor import) and am very happy with - I found the black gunk you found to be worryingly "moist" maybe humidity or liquid?
Anyhoo, to address a couple of things you talked about, The main reason I bought monitors was for composing, mixing and mastering and specifically the "balanced audio" part (Would be great if you could do a vid on balanced vs unbalanced audio!). Most peeps buying monitors will probably be eyeing up an external (or internal) Audio interface, which in part answers your "I prefer mine with the volume knob on"
Mine is a Roland Rubix 22, which you can see in the images attached.
Keep up the awesome work,
Nicky.