My boat is a 92 and I just wax it and it looks pretty good. If I am not mistaken all yhe waterlines on Catalinas are vinyl tape. You can purchase new tape from Catalina Direct. It is a little work to get the old tape off but pretty easy to put the new tape on.

I think your waterline is molded in. We had a C30 from the mid 80's with a fading waterline. Tried a lot of things, but nothing really held up. Finally ended up painting it with topside polyurathane. Even with a very fine brush, brush marks were visible, but it looked great from a distance. However, I found that the urathane would flake off in some areas and that it needed new paint every few years.  Our C36 has a molded in boot stripe about an inch abover the waterline. Beneath the rubrail is some decorative tape which has held up well- but it's some distance from the water. 

I think for the most part all waterlines (Boot stripe) are molded in gel coat  and it was the same with Catalina 30. I use rubbing compound on the boot stripe annually and then wax, It has scars that show when close by, but looks great for a boat 24 years old. If really bad you can actually sand with wet sandpaper (very very fine) than use rubbing compound.

Webb Chiles has what he calls the boat length rule.  If it looks good from a boat length away then it's good to go.  For boats older than 5 or 10 years, I think it's a good rule. 

I got rid of the narrow white stripe at the waterline when I re-did the barrier coat a few years ago, it constantly looked terrible with scum, algae and petroleum stains on it all the time.  The blue stripe I just buff and wax yearly as I do the rest of the hull.  Looks great for about 3 days after launch, then it all starts again..... 

There used to be car wax that was designed to restore specific dark colors (black, blue, etc.) You might want to check Pep Boys, NAPA or places like that.

I do what everyone else does... wax it a couple of times with a cleaner wax and off we go.

To restore just use 3M 2000 grit rubbing compound and high speed buffer, we restored two stripes back to new. You can buy a variable speed buffer at harbor freight and the buffing pad and compound at any good auto supply store.

Chic Lasser

Past Commodore