What he did recommend, though, was that when leaving the printer for an "extended period" (undefined, but I don't print much any more) the cartridge carrier should be moved to the centre of the printer away from the parking place.
His reasoning is that the heads rest on the absorbent pads and that can start a capillary action which sucks the ink out of the cartridges.
Whether that is a good idea or a bad one I have yet to determine.
It's been many years since I've had an inkjet printer, but I DO remember seeing that caveat, but with no reason attached to it, back when I had one.
Much of your damage looks like it can be scraped off with a razor blade, and the rest will probably have to be the beginnings of "your new black desk."
