People who create intellectual (as opposed to physical) property, would disagree with you. Authors, for example, make their living from the royalties of the sale of their books. If you copy a book, you are depriving the author of his livelihood.Copying Is Not Theft - Official Version - YouTube
However, in the case of a discontinued product, fabricating a replacement part which is unavailable from the manufacturer is probably not going to bother anyone. If you make a few for friends, a patent owner (if it was still in effect) probably wouldn't bother with you. If you went into mass production it might be another matter (if the patent was still in effect).
Note that there are several kinds of patent-infringement lawsuits: There are lawsuits when a company feels that its business is being cut into. There are lawsuits brought by people hoping to make money from the lawsuit, even though they are not actually in business to produce anything. (There's actually a whole industry devoted to obtaining patents and then looking for people to sue, with no intention of ever making anything with the patent.) And there are lawsuits files solely to harass someone who is disliked for a reason unrelated to any actual infringement.
In this case, I think you have nothing to worry about, for reasons the other posters have mentioned.