When checking the oil level in my 6718 today,the oil came out and started over flowing from the dip stick. The oil is black and not milky which I think rules out that any water is getting in? I think it might be diesel getting in as it does look a bit on the thin side. The tractor was running and driving as it should with out any visable problems.Has anyone had any experiene with this happening and any advice on putting it right will be very helpful? Thanks.