Hello, After my sold Sl 500 had problems – with approx. 120,000 km tandem pump and immediately after that valve block renewed – I would like to prepare now. Recommendation Mr. Hehlhans and Zädow to change the oil every 5 years or 30.000 km plus additional filters. I have now 11 years and 78,000 km – so anyway already late. Oil color light brown smells not yet burned. What’s your opinion? Happy holiday from Austria Dear greetings Henry