Previous to 1982 (when they started making owners manuals for each individual vehicle), the owners manuals would be for multiple cars in the Buick model line.
The Buick Century and Buick Regal would often be the 2 automobiles contained within this single operators manual.
(and in some years the Century Estate Wagon was included as well)
If you’re looking to acquire an original factory book like these, they can usually be found on ebay for less than 20 bucks.
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1978 Buick Regal owners manual:
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1979 Buick Regal owners manual:
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1980 Buick Regal owners manual:
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1981 Buick Regal owners manual:
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