If you really want a mower to last long, Brand is not important. A industrial quality mower is far better. The kind used by Cities, parks, and landscape companies. Industrial grade mowers far outlast "homeowner grade" mowers. They are costly though. ...
10w30 and sae 30 are both 4 cycle oils. I use 10w30 in my sears garden tractor because I use it in winter for snow blowing. I've never had an oil problem. Does it smoke?
check your local classifieds; check with a dealer who takes trade-ins. Check with an on-line site such as Craigslist or the auction sites for completed sales.