Spetz, I had dinner with one of the chemists who worked on Magnatec when it was being introduced.
Castrol's UMA (Unique Molecular Attractant) is a type of ester that clings to metal surfaces...very unlikely to be a sludge/varnish producer.
Interestingly when they were testing Magnatec, they were comparing it against Mobil 1 (think it was 15W-50, could have been 5W-50), in sequence...Mobil...flush oil...test oil (magnatec)...flush oil...Mobil.
To get before and after baselines to see that the engine hadn't changed.
They found that the Magnatec "film" carried through to the Mobil test runs, affecting them also.