If you are confident the "still shiney" areas have been thoroughly cleaned, then all the matte appearing areas (which surely, you just recently cleaned) have missing clear coat.
In that case, I'd recommend you either re-apply the clearcoat to the areas that have the missing clearcoat (if you can find a good enough OEM-shininess match on the clearcoat, with the clearcoat also being a leather-specific product), or otherwise you could plan to re clearcoat the entire wheel (this will reduce the need to get a perfect sheen-match on the clearcoat finish, if you do the whole wheel).
There are two methods of applying leather finish: wiping and spraying. Wiping can be done with good results, and may have less investment required for the application equipment, but will probably need more experimentation (be prepared to strip failed attempted before getting it perfect) to get the proper procedure figured out. Spraying is more equipment and setup work required (probably need to remove wheel from car, and mask off areas to not be sprayed), but is easier to get a uniform finish. Also, if you go to the effort of spraying the whole wheel, considering stripping off all the old finish, so you can lay down a completely even and uniform finish. Stripping the finish is a little frightening because there is a lot to remove and you will quickly feel "fully committed" (and like there is no turning back
) , however, by chemically stripping off all the old finish, you will retain the oe-style leather "grain", whereas if you don't you may find edges of old finish, or if you use very fine-grit sandpaper to smoother down edges of the original finish, it will leave you with an "unnaturally smooth" texture.
Another option is to apply black dye, rather than clear, and I can tell you there is a Kiwi black leather dye product readily available that will give the perfect OE black Porsche shift knob/steering wheel shade
as well as a perfect "shininess" match, but the main drawback is when you clean your steering wheel with an aggressive leather cleaner, some of the black, outermost finish will keep coming up on your cleaning cloth as a noticeable black substance removed, and you'll haven hard time realizing if it's dirt being cleaned, or the black outer layer of the finish. (It's also more of a problem to refinish the shift knob by dyeing it black, because if it has contrast color stitching like mine did - and I've not seen contrast color stitching on an OE boxster steering wheel so this probably won't be a concern for you - then topcoating with the black dye will alter the color of the stitching to black.