we will be using our TTHP 17 hp Kaw Exmark again today for the 2nd time for about 2 hours.......so it will have about 4 hours on it.....We plan on changing the oil the next time we mow (6 hour mark). The book states to change the oil at the 8 hr mark and I noticed you told someone the 5 hr mark. My questions are: do you recommend a certain brand of oil? We checked with the dealer to see if it was permissible for us to change the oil and he said would not void the warranty. And do we need to change the oil filter at the same time, or just the oil? Thanks for your help.