So the best you may be able to do is to report that this service panel is of a type for which a number of problems have been reported over the years, and recommend that an electrician be brought in to conduct a detailed inspection. Meaning no disrespect to, or unkind reflection upon, yourself or other members of your profession, I think it is too much to ask of a Home Inspector to discern the difference between an old, but still functional panel, and an old panel that is about to fail. You should leave it up to the seller and any prospective buyer to decide who pays for the electrical inspection, and who pays for any repairs or upgrades that may be recommended by the electrician.