Have you ever used an engine oil analysis service? I haven’t, but I do have a few friends who swear by the practice. Apparently, all you need to do is send a sample jar filled with outboard motor oil to a specialty place and then they run a full analysis to figure out the condition of your engine.
Upon further research, it appears that engine oil analysis is something frequently done by fleet operators. Taxi companies in particular condone the practice because it helps them figure out how often they should be changing their oil and parts, or even replacing cars in their fleet. The aviation industry also uses oil analysis to get a better sense of what is going on inside of their jet engines.