Depends WHAT contaminates you are removing from exterior trim. If it is tar or asphalt, Goo Gone has worked for me. I now use Krud Cutters Ultra Power Super Adhesive Remover, which is like Goo Gone on steroids.
If it is concrete from road cement repair or new construction, regular Coke -Cola(not Diet or Zero) kinda works. Yes, there is a specific concrete dissolver called RoMix Back-Set, but I you will need to find a supplier for it. Now defunct Top of the Line Detailing Supply used to sell it.
If it is road marking-striping paint, then Goof Off OR 3M Adhesive remover can be used with the caveat that it MAY turn your black plastic white or light grey.
I would use Optimum's Power Clean diluted 3:1 for general cleaning and an old stiff-bristle tooth brush or a small nylon or tampico fiber bristle brush (NOT brass or stainless steel!) for brushing trim as needed. Follow with a damp clear water microfiber wipe and it should be ready for trim coating or restorer/protectant.
My guess is that M39 HD Vinyl Cleaner was supplanted/replaced when the Pro Detailer Line D101 All-Purpose Cleaner came out. It is another APC you could use to clean trim diluted 4:1. Just don't use that dilution ratio on coated leather! It has removed some dye color for me in my experience, which is why I use leather-specific cleaners now.
I also think Solution Finish sells a specific trim cleaner to use with their trim restorer, but I think it is only in 4 ounce bottles.
I just called and they've discontinued it with no plans for a replacement. Glad I stocked up as it's basically all I use for that.