I think its a California thing to get pre-paid maint. lots of dealers out here advertise it. One of my chores as a kid was changing oil, bleeding brakes, checking fluids etc etc. So Ive always done my own maint. kept receipts never had issues with warranty. Some mfg require genuine OME filters, I think in the CLA book I read we recommend only using Benz parts, and if small print but if you dont it wont void the warranty. I think if more people knew how easy oil changes are more people would do it.
Id change oil for a lot of friends one car I had to remove the left front tire to get to the filter it was years ago, anyone remember what car it was?