I have a friend that works for a major oil company and he's thinking about starting a business where he sends you a free kit, you mail back a sample of your oil, and then they use a spectrometer to analyze over 30 aspects of any oil for cars, boats, motorcycles and more.
He would probably charge about $21.00 per test and you would be able to log into a website to check your history. He can tell you almost exactly what bearing, seal or whatever might be wearing out. His company currently does these tests for companies with large fleets of vans, trucks, heavy equipment, etc.
He can check transmission fluid, differential fluid and motor oil.