Alright, sounds good. That kinda sucks, I was hoping to use it, since it doesnt leak at all. I haven't got into the cable, as most of it is under brittle trim, and headliner. So with that, what is a decent nmo antenna?
If you are carful, you can remove the mount from the outside of the truck. There will probably be a bit of slack in the original coaxial cable.
Carefully cut the coaxial cable where it enters the old mount.
Attach the new coaxial cable to the end of that -very-securely-
Now —carefully— start pulling gently on the radio end of the old coaxial cable.
If you are lucky, you can pull the new coax cable in that way.
A properly installed NMO mount will not leak. I've been installing them for 30 years and never had one leak.
A really good NMO CB antenna is the Larsen NMO-27. I have one of those that is about 30 years old and still works like new. It's hit a lot of tree branches and low parking garage on the top of a full size truck and has never let me down.
If you want to do this right, don't cheap out on components. There are low cost ham/hobby grade antennas and mounts out there on the market. Yeah, they'll work, but for a few bucks more you can get the higher quality professional grade stuff. Stick with Larsen, Laird, Antenex, Comtelco.