String Trimmers

I have a weedeater FX26A featherlite trimmer that I have had for 5 years and it works great, easy to start, runs good, however recently the head started making screaching noises and now the head has dropped down from the shaft about 1/2 inch. I took it apart and greased everything and put it back together and it worked for about 20 minutes and then the head dropped again. I suspect that it is the bolt that attaches to the cable. The hole looks a little rounded. They tell me that I can't buy that part. Any ideas. I love the trimmer, but can't put up with this any longer.