I refurbished two 2230 silver plates for a fellow collector here on AK who just let me know of this thread. Fortunately they were not engraved as this would have thrown an additional challenge at me. The fill and wipe suggestions might prove problematic for two reasons. First, the ridges in the brushed finish will hold your font paint especially if you thin it down. Second, whatever you would use to wipe with must be extremely flat and yet be able to absorb the excess paint which tends to make you want to push harder thereby removing much of the paint in the areas you need it to remain. Also, you would find that black, semi-gloss paint will dry or cure to more of a flat finish if you wipe it before it has set up.
BTW, the two plates I refurbished only needed the fonts removed, and re-screen printed. The plates were in excellent shape otherwise. My comments as to refurbishing the plates themselves are from much experimenting with other Marantz plates I have from parts units. I have even purchased abused plates off Ebay to experiment with to determine the sand grit, sizing and anodization methods that yield the best results. With regard to sizing, or sanding the grit I have determined Marantz must have used #180. It seemed a bit coarse to me at first but #220 just didn't produce the same result. If you think about the process under production it might explain the subtle differences among plates of the same model as I have multiple units of various models which I have placed next to each other which brings these differences out. I say "process under production" as Marantz contracted for the production of its components in the hundreds if not thousands so a fresh #180 paper will yield a slightly different result from the 1st plate sanded to the 50th plate in a production run. This is because as the sand paper is used its "tooth" or bite is worn down. I would first use some scrap aluminum if you are on the right track, as well as wear down the initial sharpness of the sand grit until you see what you are after. Although setting up a sanding jig and doing this yourself is an option keep in mind under production these plates were fed through a large sizing machine that applied an even amount of pressure on the plate as it passed. Aluminum is soft so you may want to fabricate a stiff backer plate to use instead of your hands. Otherwise you may find that the areas where you are holding the plate will get sanded through first. The tendency then is to keep going until you move your hands around enough to sand the entire plate only to sanded too much material off especially if your plate is engraved.
To remove the existing fonts/paint off the plates I got beyond the fear of damaging the anodized clear coat and discovered paint remover works best. Do this in sections where you can wipe it off as soon as it bubbles off the surface. Do not let it dry again as you wipe so moisten your cloth with thinner or minerals spirits ahead. You might even try a toothbrush to get into the engraved surfaces.
Regarding the application of paint I had no success doing it myself so I found a typesetter to duplicate the Marantz fonts and created a digital file for use by my local screen printer use. The paint he used was an epoxy (two-part) semi-gloss black for its durability. The plates came out fantastic and my customer was extremely pleased with the results as you really could not tell any difference from the originals. Evidently the 2230 does have an issue with font wear as this unit has some pretty small numbers. This is getting a bit lengthy so I will stop here and see if you have any comments.