Keeping your engine under 3500 rpm is asking for trouble. such as excessive carbon and varnish build up. I even bet the life of your Cats will be reduced. If you were to go out and really let the engine work hard like flat out for a mile, you will get a rotten egg smell which is from your Cats. You need to clean the engine out by running it the way it was designed and you won't need any sea foam. Also Mercedes doesn't actually recommend 0 weight oil anymore. I would recommend 10 wieght which is what I believe MB now recomends, 10w will quiet your lifters a bit.