I have a quarter size chip on my windshield which started out several years ago as a nick. I've een told that there are glass specialists that can repair this, is that so? Has anyone ever had this done and is it a reliable fix or does one have to replace the windshield.

If the chip is in critical area (direct line of vision) then it is best to replace the w/s.Even the best repair can still be seen at certain angles and cause a distraction,also if there are runs coming from the chip in excess of one inch you should replace it,that being said,I have done many w/s repairs with great success.The windshield repair kit can be purchased at any good parts store and is an easy DIY fix.
Tip:1 pick a dry day you don't want any water in the chip when you fix it because water trapped in the chip could later freeze and cause a crack.
Tip:2 ultra violet light cures the resin that you will be injecting into the chip,so you must do your repair out of direct sunlight and then move it into the sunlight when you are done to cure.
Many glass shops and some oilchange places will do rockchip repair for a fee.If you have trouble finding anyone in your area try calling a used car lot,they should have the phone number of a mobile service,expect to spend anywhere from $20-$75.00 or buy a cheap DIY kit it is pretty easy.good luck