My mag mount base spins as I tighten the antenna. It will tighten about 3/4 turn, the break free after 1 full turn. Do i need to replace it?
Probably best you replace it. It sounds like on of the retaining bolts inside has come loose from maybe bouncing around on the vehicle. You may be able to pry off the rubber backing on the bottom and get at the bolt, but that may or may not work, and you may not be able to get it back together again….and that is just a guess on the problem. So my recommendation is to get another mag mount.
I agree with Harry. UNLESS YOU KNOW how to fix it, time is money, Just get a brand new one and keep all your receipts.. Mag mounts are not that popular and you should get a new one pretty cheap.
Here is an COMET dual band
https://www.gigaparts.com/magmount-antenna-16ft-coax-ma-721.html
Enjoy
Doug