Lost My Oil

[nirecap0]

Last Fall I purchased a new to me boat with two Yamahas. Over the winter the 150 2 cycle (150TLRT) pumped all of the oil from the auxiliary oil tank through the motor and onto the ground. The oil tank on the engine was full. How did that happen? The authorized Yamaha dealer in Portland told me that one or more of the check valves were dirty and needed cleaning. This was done ($238 later). He told me the main power switch was left on and the pump on the auxiliary tank pumped the oil out. It did not make any difference if the key was left on or not.
Yesterday I took it for ride and once the engine burned out the accumulation of oil in the cylinders it still ran oil rich (smoked). It does not appear to be fixed. I did not run it long enough to get an accurate read on the oil consumption.
Is it possible that over the winter the oil siphoned out some how? Through pressure in the tank or some other mysteriwes means?

[99yam40]

I believe that if the battery voltage to the oil module gets low it will not turn off the pump even with the oil level switch showing it is full