I did my first oil change on our V70 at 90 000km (done by Volvo workshop before) and found brown rubber-like deposit on oil stick, filler cap and in the filler on the valve cover. It does not look very nice and I assume there is more of it inside the engine. The car has been run on high-quality syntetic oil since new... I suspect that the 20 000km oil change interval on the -00 and later engines is simply too long? Or is there any other reasonable cause? The car is mostly used for commuting typically 30km. Would it be a good idea to go for 10 000km oil change interval instead? All suggestions are appreciated.