I'm a bit of a novice to this, so please forgive if this is a dumb question. I don't doubt the usefulness of UOA's to see how well an oil is holding up against viscosity breakdown and engine wear. But it seems to me that a very important property of the oil is its to keep things clean and to not allow varnish or sludge to form. Is there anything in a UOA that gives an indication of this? I ask because my previous car was a 2001 Toyota Corolla. Not a known sludger, supposedly. But from probably 50k on there was visible varnish and even some dark brown material visible on the dipstick. I wasn't great with the maintenance (too many other crises going on in my life at the time), but it did get regualr oil changes at not more than 4500 mile intervals at a Valvoline quickie place. By 120k miles, things were beginning to get serious. I think shorter intervals, or maybe synthetic oil, were called for here, but I thought that what I was doing was reasonable at the time and it easily met Toyota's requirements. Would a UOA have caught this?