Disappearing oil mystery on 2004 Johnson/Suzuki 140 4-stroke

[ggduff]

Last spring I took my Johnson/Suzuki 140 4-stroke to my local mechanic to get an oil change. Since then I've been losing oil. About every 8-10 hours of operation it will overhear, go into panic mode (cap out at 3000 rpms) and even shut off. I'll check and sure enough I'm almost a quart low on oil. Unfortunately my low oil and no oil indicators are not working. Hopefully I have not caused any damage after this has happened 4 or 5 times. When I top off with oil and restart, everything is fine. What I don't understand is that with losing this much oil I have never seen one drop of it in the water. There is no evidence of it anywhere I look on, in or around the motor. I asked my mechanic about it and he said that 4-strokes burn oil. I'm not buying it. Any thoughts on what it could be or where I would even begin to look? Thanks for any thoughts or advice.

[boats.net]

It has a low oil pressure warning and a overheat warning. The oil level on dipstick will be low if checking oil when first turn engine off, need to shut engine off tilt engine up to top porition of trim range and let sit for at least 5 minutes before checking oil level to allow any oil in engine to drain back down into oil pan, trim engine back down until is level and check oil level on dipstick. If oil level on dipstick is anywhere between the lower and upper line don't need to add oil.
Need to have compression test done on engine, test oil pressure to see what warning is being activated.