Rolls Royce cars and Rolls Royce engines have been separate since the 70's but because by Parliament law they can share a name and a badge, people associate them as one.
The issue here is GM ruined Saab. Saab was an engineering pioneer. In some ways, Saab cars were more revolutionary than Saab planes. For example, the Saab 92 and 93 (Not 9-3) gave the industry new aero and engine advancements. Especially Saabs use of two strokes. Saab is still considered one of the most accomplished marks in rallying before the WRC era began.