Why buy new ones if the old ones are working fine? Unless an oven was completely shot, I would never get rid it, because the chances of the replacement being of comparable quality are pretty slim, imo. Oven manufacturers love to replace quality components with cheaper ones. It doesn't all happen overnight, but, in the span of a decade or more, it's pretty rare that an oven stays the same. This is, unfortunately, true for pretty much everything these days, but it's especially true for ovens.