TimL- If it's not so far gone that it needs refinished with the ETR kit, you can try what I do:
-Clean with Griot's Rubber Prep, scrubbing until no more dirt/dead material/etc. comes off
-Seal with something like Utlima's Tire and Trim Guard Plus (UTTGP). I like two or three coats
-Maintain with ValuGard's Fast Finish QD, which I find leaves the *perfect* level of sheen for black trim. Just spritz some on after the wash when you're drying it off
You can skip the middle/sealant step if you like, I'm doing OK on some trim using just the FastFinish, but it'll take more work at each wash. With the Ultima on there the trim is basically maintenance-free for an extended period.
Another approach that works OK for me (but not as well as the above) is to clean/prep with KAIO and then protect with either KSG or Collinite 845. I did it that way for *years* until discovering the Ultima sealant. You'll need to redo it, starting over with the KAIO, every so often.
So I use either a trim sealant or an LSP-based approach. I do *NOT* use dressings on such trim.