Sea Ray

I own a 2011 200 Sundeck with the 5 liter Mercruiser V8.  We keep it on a lake in NH at our lake home and use it perhaps 40 hours a year.  It is in great shape.

This year, on my first ride of the season, I received an alarm for an oxygen sensor problem.  I took it to the local marina for service.  They replaced the starboard O2 sensors as indicated and took it for a water test.  After 30 or 40 minutes, when the service tech was ready to declare success, it went to alarm again for the O2 sensors.  He replaced the port sensors and tried again.  It once again alarmed...all four sensors have been replaced.  He called Brunswick (I believe) and was told to reflash the ECM and did so.  It seemed to work.  I picked up the boat on 7/3 and ran it for about an hour with no problem.  Two days later I started out on a ride and the O2 sensor alarm came on again.

This is nuts.  I'm $800 into this problem and I'm no better off than when I started.  I've read some complaints about O2 sensor issues in various forums, but I haven't seen anything helpful.

Has anyone had this problem and managed to get it resolved?