This is almost off-topic but not quite ~
I'll re-affirm the opinion that if the oil meets spec's the manufacturer can't void warranty -

I had a new Deere riding mower that, after only 30 hours use or so, developed a huge knock (I think the mech said it was the "bottom end", i'm not a mechanic, dont' know exactly what it was)
Long story short û The dealer said I caused the damage by using the wrong type of oil. When I showed them that I used the 10W-40 it listed as approved in the mowerÆs manual, then the service manager said (this is so much crap) that the manual was wrong AND that I had to pay for 2 of his mechanics (one hour each) for removing the 10W-40 and putting in the correct oil, which was 10-40.
Well, I hit the roof, called a friend of mine who is a lubrication engineer and he said they were full of crap, I called the factory in Wisconsin and talked to someone there û
Bottom line is they put a new engine in and if the oil is listed as approved, the warranty has to be honored.
BTW, that was the ôGreat Outdoorsö John Deere dealer in Des Moines, Iowa. Avoid them like the plague.