Mercury 150 xr4 problem

I have a 94 150 hp mercury xr4 with a supposed oil supply problem. The alarm for oil misture stays on during speeds in excess of 10 mph. Have had the sensor in the oil supply tank changed last year, and the alarm was fine for 4 months. Now again above 10 mph the alarm stays on. A marine repair shop says the oil supply drive gear is worn and may be replaced for approx. $1500.oo , or the other option is to mix the gas and oil in the fuel tank each time. Anyone familar with this type of problem with the mercury 150 hp?

I had a smaller Merc with the same problem. Was told the gears were one plastic and the other steel. The plastic one wares down thus putting too much oil in. Only two choises new gears or premix the gas. Well three realy ( new motor ) Hope someone else has better info. Jim ps make sure oil tank is full all the time.