I know that Ryder burns up to 5% mixture of drained and filtered crankcase oil. They do extensive research on all things like this. They can justify this because they have the second largest vehicle fleet in the world, second only to the US Government. Many over the road rigs you see belong to Ryder. If you will look on the trucks you will often see a little R Ryder logo somewhere mixed in with their various numbers painted on the cab.

I did this some years ago for awhile with my 240D and had no problems whatever. I just stopped doing it because I found a convenient place to turn in my used oil.

Good luck,