Aerial fixing - for Shipmate radio on 36cc

Some help please. My 36cc is a 1999 model and the radio fitted was a Shipmate. The aerial at masthead is the fibreglass type with the metal aerial 'inside' the fibreglass tube. The problem is that the fixing nut seems to come loose. The first time the riggers went up the mast they tightened the fixing nut, and all appeared well. 3 months later the aerial 'fell off again'. The radio still works fine. The riggers went up again, and this time they say the thread is stripped. They recommend a new aerial, and if I dont want a join in the cable to the radio will need to rewire right back to the chart table. There must be other options...so any ideas appreciated.