Lent pressure washer (B&S 4 cycle, 6hp "Quantum" engine) to co-worker.
Co-worker checked oil, saw it was low, and added *2-cycle* oil. Ran
unit for another 5-10 hours.

Pressure washer came back a mess. Oil residue all over the place. Saw
seepage from what looked to be bottom horizontal seam of engine block,
and residue all over front of unit, and even in air filter (?).

Haven't ran the engine yet. Drained oil last night (after a fight with
the bottom plastic under-cover to access the bottom drain plug). Will
change spark plug and air filter today as well.

Is there additional maintenance I need to do (a gas additive?)?

Is the engine going to die prematurely or something?

Thx,
Oliver