There's no precise number for how many 1978 Cadillac Eldorados were produced, let alone how many of those were specifically El Dorados (the "El Dorado" name was applied to a range of models that year, not just one distinct car). Furthermore, knowing the production numbers wouldn't directly equate to rarity, as the surviving number is what truly dictates rarity. Many cars were scrapped or destroyed over the years.
To summarize: Determining the rarity of a 1978 Cadillac Eldorado is difficult without more specific information (trim level, condition, etc.) and access to detailed production records which may not be publicly available. They are not exceptionally rare compared to some other classic cars, but finding one in excellent, original condition would certainly be more uncommon.
