I had similar problems with my Optimax 225 recently. I tried all of the fixes with different sensors and bypasses etc. Then recently I found a fishing forum where someone with a similar problem fixed it by replacing the battery (Optimax apparently require a minimum of 1,000CCA). I had never had problems starting my engine and always seemed to have charge in my battery (My battery was one year old and rated at 900 CCA). I was so frustrated by the problem of constant alarms and limp mode, that I thought that I would try this solution. Swapped the battery out for a new one rated at 1,100 CCA and have no alarms since.
It seems that the battery was sending "ghost signals" to the ECU on the engine and the ECU was interpreting it as an oil problem and triggering an alarm.
May be worth a try. Good luck.