Good morning Wguinon,
Thank you for your inquiry. Based on the information you provided it sure sounds like the issues is likely with the Radome. Couple of things that could cause poor sensitivity would be a failing Magnetron or the MIC. You could contact one of Furuno's authorized support dealers for further troubleshooting and evaluation or you could send the Radome into a service center for further evaluation.
Where is the vessel located?
C-Bass.