help please ,om my ariens ht16 my motor kohler magnum twin vert. 16 hp.there is a ticking on 1 of my cylinders .i was told it was the valve seat that came loose. i was told that these cant be peplaced and i need a new motor.... is this true? the mech. didnt look at my machine he is going by what i told him.that 1 cylender the plug has more carbon than the other and ticks.