Small Engines (Lawn Mowers, etc.): SEARS EZ3 143.966500, crankcase pressure, engine crankcase

Question
The model was purchased from Sears Canada-6 1/2HP,self propelled. I believe it is a Techumseh engine.It is about 10 yrs old and given no trouble all.Monday I started it wit with some difficulty, and when it started it was pumping quite large volume of smoke from muffler.I noticed droplets of oil on deck under muffler.Wed, I pulled off muffler and there is some oil drips there. Crank case shows a little oil, not much.Oli level was just below max(never overfilled).Air filter was v.dirty, so I removed it and tried starting engine, giving it 5 pumps on primer bulb.Engine fired quickly and ram very clean for about 5-10 secs, then got progressively smokier until I shut it down after about 30 secs. As this is 10 years old I'm wondering if it's worth repairing ,if it might be rings/valve guides? Your assessment and advice would be greatly appreciated!

Answer
Did you tip the mower to clean under it or to sharpen/change the blade?  If so you ham have run oil into the engine crankcase breather.  This is in the top of the crankcase, held on with two screws/bolts and vents the crankcase pressure.  Remove and clean or replace including the gasket.  In some cases there is an up and down to the gasket so the drain hole lines up.  Next check the oil fill o ring.  Next check the dipstick o ring. See if oil is leaking from the crankcase gasket.  Repair or replace as necessary.

Good Luck