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as it seems to dislodge gunge that is actually holding stuff together
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There seems to be a little misunderstanding there. The sludge is there but it is not holding anything together. Imagine that -sludge holding together something that has to handle 300-360BHP.
New oil have cleaning and other additives that hold sludge and wear particles in the oil. As the oil ages it looses its properties and sludge settles out in corners and crevices where the oil flow is slow. When you put fresh oil in it's cleaning additives start dissolving that sludge and lifting it up in the oil. The problem arises if some of that sludge instead of slowly dissolving in oil detaches it self from metal parts in lumps as the fresh oil seeps between sludge and metal. These lumps then can block oil passages, small wire mesh filters or get jammed in solenoid valves or between disks.
We were experiencing similar problems in Latvia in the 90's with car engines. Old Soviet cars that have been running on primitive USSR motor oil had a lot of sludge build-up in the engines. I have taken couple of those engines apart in my teenage days and couple of mm rubbery/jelly build-up on the most of engines inner surfaces were quite normal, 5+ mm in tractor and diesel truck engines. When the modern western oils become available in the start of 90's a lot of people killed their engines using modern oils as they lifted up sludge in lumps and blocked oil passages in block, head or crankshaft stopping oil delivery and seizing up bearings.
If I get that oil from sarg I am thinking of draining just a couple of litres of oil and replacing it with fresh oil so that it hopefully washes it slowly and does not lift up any lumps. Then another couple of litres later and then possibly a full change with filter some time in the future. Still not quite sure if I will be doing it. If the gearbox fails it will be a good excuse to do a manual conversion.