I use 303 on door jam sills, side skirt and all black rubber and plastic trim. I apply using a small terry applicator(those used for waxing), wait awhile (15 minutes) then remove. Trim looks nice and black, no shine, maybe a tad bit if any! for the most part it makes them very black! it lasts a few weeks also. It really does a fantastic job on keeping seals around doors/trunk and compartments soft and like new. I have been using it for a few years. My car is a 94 acura my seals are very soft, before i started using 303, they were a bit brittle. My dash and panels also look great, even when dirty, friends say wow you keep your car nice! it's because they are looking at the very black dash (not grayish), with 303 on it. I notice when my dash gets a little dusty or its time for an exterior wash, I could sometimes just wipe down the interior without dressing, still looks great!
I also use 303 on for all interior dressing also .
If your trim is in bad shape you may need to forever black or some kind of permanent fix.