I don't know; seeing as they've been simply blocked in, they might look pretty good with the application of a simple wash!
Some of my earliest metal minis were painted straight over the metal too. They looked great, but the paint rubbed off by just looking at them. So I only ever did the one squad like that. Afterwards, I always primed my models. At first by simply brushing on, later, when acrylic spraypaints became more affordable and available, by spraying them.
Whether or not to repaint is up to you and your nostalgia. Me personally, I've made it a point to never repaint my old miniatures, because they represent the pinnacle of paint skill at that particular moment in time. They might be cringeworthy now, but I was mightily pleased with them back when I finished them.
So unless you intend to use them along other miniatures in a new project, I'd leave them as is (or with a quick wash of Armypainter Strong Tone perhaps

), but that's just me.
As for Dettol; I've never used the stuff, and I can't recall if it reacts with plastics yes or no. I have used DOT4 brakefluid in the past with OK results, and Simple Green from the US, with awesome results though...
But what is that on the last guy in the thunders squad?
Plasmacannon, 4x Heavy Bolter and 2x Multimelta in the second last picture (left to right), and the loose gun is another Plasmacannon of a slightly later design
