Excellent explanation. Very true. I just change engine oil every 7000 to 9000km but service people including Toyota company ( I have a Toyota Camry 2015ed.)recommend oil change at 5000km. My Wagon R gets an oil change every 10000km and I use Mobil semisynthetic. My Honda CRV indicates the oil expiration so I have no choice but it happens after about 7000km. I never allow people to wash my cars as it will lead to scratches on the paint. So I do by myself as it is sort of relaxing experience!
I have Skoda Octavia for 15 years l have never done any service at service station . Every thing I did at home even oil change I never wash engine room you are 💯 correct