CO Experts monitor shows Peak around 20PPM, Mechanic cannot find any issues

[saldarro]

I have owned a Piper Dakota for 14 years, a few months ago I got the CO Experts monitor, I get alarms showing Peak around 20PPM.
With the vents closed and heater/defroster open I smell something like burned oil/exhaust odor.
My Mechanic did a complete Annual and looked for potential sources of CO but cannot find any issues.
The full exhaust was replaced about 7 year ago = 700 hours ago.
Thoughts?

 

[magman]

 

[GM.]

 

[Dennis]

 

[jvos]

 

[piperowner]

 

[Orest @ CYFD]

 

[magman]

 

[magman]

 

[GM.]