The thing is your servicing a sealed unit, a unit that is a sealed unit for a reason. The unit your doing preventative maintenance on should out live the mower itself without service or it wouldn't have been a sealed unit in the first place. Your talking about a homeowner unit that probably wont accumulate 30 to 35 hours a year and if your mower has a decent warranty say 3 year 180 hr which ever comes first type of thing it should out live the warranty and if it doesn't it's there problem to fix or replace, if it does out live the warranty chances are good you'll probably never have an issue with the unit for the life of the mower.