This would be my preference too Rado. A good quality engine oil will have a robust additive package including a generous dose of detergent "sludge dissolver". However this will be nothing like as aggressive as that found in a specific engine flush product. My assumption would be therefore that it will act more gently and slowly on the deposits and therefore reduce the risk of overwhelming the filtration system.
We bought both our Panda and my boy's Punto around 3 years ago and, as neither vehicle had any record of the timing belts having been done I changed both within about a fortnight of each other. I removed the cam cover on both engines to check the timing and was pleased to find the Panda was absolutely spotless inside but the Punto did have some sludge build up. I put the Panda on a normal, once yearly, oil change regime but the Punto I changed the oil on every 6 months for the first 3 oil changes. The Punto oil got "dirty" quite quickly over those 18 months, less so on the 3rd change though, so it now is on a once yearly change interval (does around 6 to 8,000 miles a year). It's oil still gets dirtier than the Panda, but it does more miles too, however it's not really "black" like it was to begin with so i think most of the crud has been shifted, nice and gently, by the regular oil changes. It'll be interesting to see what the inside looks like when I do it's cam belt again next year.
The only slight downside to doing this is that you are changing the oil more often so it's costing you and you need to still use a "good" oil to get the advantage of a robust additive package so you can't save money by buying "cheap" oil. I still much prefer to do it this way though because of the "gentle" way it cleans. I've worked on cars since the early 1960's and, after being convinced by one of my college lecturers not to use flushing oils in most cases, I've treated "dirty" engines in this way with generally good outcomes. Having an interest in older vehicles I have to say though that nothing beats an actual strip down and a good clean up in my local electric motor reconditioner's heated chemical degreaser plant! Not a very practical course of action unless you are rebuilding an engine though.
Oil sludge sounds like we are talking about a jelly like substance which would be easily dissolved and liquidized and so allowing it to come out when the oil is drained? It just occurred to me that some people reading this may be thinking "what's the big problem with using a flush then?" Well folks, the problem is this stuff: https://www.youtube.com/watch?v=0hQSHyymkrM Although there is likely to be a far amount of sludgy jelly there's also going to be a fair amount of the stuff in the video and you'll notice it's very far from being a jelly. The problem is that when you loosen this sort of stuff it tends to come away in clumps and it's pretty good at clogging up the filter screen in the bottom of the sump which the oil pump sucks it's oil through - not good to starve the pump. Some will get through the screen and travel through the pump - to it's detriment - and then go on to block up the oil filter. If this happens the oil filter bypass will open - a safety bypass to stop the engine bearings being completely starved of oil - and allow unfiltered oil to circulate round the engine so carrying these gritty particles to all bearing surfaces in the engine and blocking up oil restrictor jets to the likes of piston cooling jets and cam/valve gear. Allowing the sludge deposits to very slowly and gently dissolve over an extended period of time greatly reduces the tendency for the sludge to break of in large chunks so reducing the risk of overwhelming the engine's filtration system.
