Halfords classic 20/50 is good stuff - very reminiscent of Duckhams - and is very benign detergent wise. It is also good value.
This detergent thing though is a curious one. Yes, there are lots of stories, but has it actually happened to anyone here that putting clean, modern, albiet supposedly detergent-laden oil in an engine has done it real harm? I am always willing to learn but my own experience is quite the opposite.
When I had finished restoring my Dodge fire engine (it took a year or three on top of the dozen years that it had stood idle) I set off to drive it back from Hull to Cumbria. The engine on the Dodge by the way is a big version of the WC Dodge flathead 6. It went well but smoked like a chimney and had very very soon used up what I had thought was a generous reserve of spare engine oil, and although things were running well the smokescreen was continuing unabated. Faced with whatever was on offer in whatever roadside garage we had stopped at, big brother and I purchased more oil, this time Shell Helix SAE30 diesel oil (which I suspect has more than its fair share of detergent). In it went (and rather a lot of it at that) and before long I was caning the old Dodge (which always did have an indecent turn of speed) up over Stainmoor. A quick stop and check revealed no further oil consumption; there was no smoke and the engine was going like a bat out of hell. It still does for that matter and the only oil it uses leaks out of the timing covers (I really must get those sorted).
My guess is that the oil was just what was required, un-gumming things like piston rings and the like, which the "ordinary" stuff just couldn't manage in the same timescale.
I have also tried to remove gunge from inside sumps with all sorts of chemicals and tools, it is a far from easy job and I remain unconvinced that a little detergent in the oil would get results when me in my wellies plus the mother of all steam cleaners cant shift it.
But, as I say, I am here to learn so has anyone had personal experience of the new oil in old engines issue??