Bought a B&S-powered 21" self-propelled Jacobsen in 1973 ("Turbo-Vent" !!), ran it over 800/hrs per annum first few years (30 hrs week times 29-weeks). Then, constant use on one or two good-sized yards (3-6 hours/week for same seven months or 29 weeks; 130 hrs annually) in the remaining 20 years. (Or, lets say over 4,000 hours)(10,000 miles at 2.5 mph?)
Added electronic ignition sometime in the '80's, a magnetic-mount hour meter (TinyTach?), and, from new serviced air fliter and oil every 25 hours past break-in. Minimum twice yearly changes, plus plug change (mower used every month, even if only once). Straight 30W per manual. VERY, VERY careful about not overfilling. And in later years, keeping topped off.
Pri-G or STABIL in fuel canister per recommended dosage; never let get more than two months old before dumping it in one of the cars. Always stored in garage or other non-damp location.
Finally gave away at 24 years: one head gasket and carb rebuild; more wheels/tires than I can recall (plus drive belts; shoot, got too hard to find the parts anymore). Blades were unique and hard to get ahold of. Actually wore the thick alloy deck thru in one location from grass alone.
Took patience in gettin it started, but once warmed it'd still take on Bermuda without a real problem.
Was talking to repair shop owner last week after I was given a 20-year old K&S Curb Edger for him to troubleshoot. (Weedeaters just ain't the deal for the grass/concrete edging). He said todays mowers are -- for reasons he hasn't figured out yet -- only lasting 6-7 years versus my not uncommon experience.
Latest mower is cheap 20" MTD rear discharge($150 ?) plus replaced el-cheapo plastic wheels with ball-bearing steel wheels. Locked throttle at 3/4. Loves FP and LC! 8-prime pumps and starts on first tug. Gonna just buy an extra quart of 10W-30 RL next time and do an LC carbon clean prior to using it. Tiny yard, maybe two hours on a "tough" week when I walk slow, use a big overlap and crosscut. Still dump gas at 6-weeks, 2-mos, etc. With the RL and LC (plus FP) think I'll try annual changes. At 31-ozs engine oil capacity I don't think I can go wrong.
As it is, my "cost" at five years for this mower has been ($180 divided by five years plus gas/oil and service supplies), so, with zero shop time -- and it lasts even a couple more years -- I'll buy another, transfer the wheels, and keep going pretty much for "free" versus an expensive-needs factory-trained-technicians, etc mower).
And if this edger dies, I'll try to snooker my bro-in-law out of the K&S my old man bought in 1962.
Change stuff often, clean it thoroughly (no dust), touch up paint as needed, tighten fasteners, grease controls and keep two or three blades sharpened and balanced. Never let it cut grass that requires more than one-third of grass blade height removed. This is what works for me.