I think that it is a good idea to waterproof the inline connector which is used on the 9500ci and STi-R antenna cables. The procedure is quick, simple, and very effective. I should know -- I generally pressure wash my car engine and everything else under the hood every time I take my car to the local car wash. Note that I have installed petroleum jelly in all of my car engine's electrical connectors under the hood, except for any high voltage connections such as the ignition coil, spark plug cable boots, et cetera.
***** Dielectric grease, available at automotive stores, is highly recommended instead of petroleum jelly. *****
How I did it:
1. Use an ear swab to pack some dielectric grease into the female half of the inline antenna connector.
2. Plug the connector together.
3. Use a cloth to wipe off any dielectric grease which either oozed out or otherwise got onto the outside of the connector barrels.
4. Use another cloth soaked with isopropyl alcohol to thoroughly clean off the outside of the connector barrel in order to assure that there is no dielectric grease residue on the barrels.
5. Tightly wrap the connector barrel where the two barrel halves mate with at least 5 wraps of electrical tape.
6. Install two small wire ties around the electrical tape. The wire ties will prevent the electrical tape from unraveling over time due to engine heat.
This is what the inline connector should look like when you are done: