Did my first oil change @ 25 hrs with a synthetic/conventional blend. I just read elsewhere at this site about using a NAPA Gold #1516 oil filter in place of the Briggs. It supposedly has the same specs with a larger volume @ a cheaper price. I think I'll be looking into that on my next oil change.
I was lucky enough to find a mower that had a serviceable transmission. Mine if from HydroGear, and it has a drain plug, a filler plug, a level plug, and a spin-on type transmission filter. I changed the oil and filter last season and used Amzoil 20-50. So far it has been perfect. If you follow many forums you will see many folks have purchased mowers with "non serviceable" transmissions, the transmissions fail and they are faced with a minimum of $300 to repair it, and then they still have the weak trans they started out with.