Vehicle dashboard cameras or dashcams, among other smart vehicle technologies, are increasingly attracting interest across the globe. Furthermore, dashcam videos as objective witnesses are often shared to resolve various traffic incidents. In this work, we aim to understand cross-national differences in motives and privacy concerns of dashcam video-sharing, which are closely related to the factors that vary across countries, such as cultural values, traffic regulation, driving environments, and privacy perception. Toward this goal, we conduct a cross-national survey study with three countries with high dashcam adoption rates, i.e., China, Korea, and Russia. The survey results from these countries consistently revealed two major motives for sharing dashcam data: (1) reciprocal altruism and social justice, and (2) monetary reward. Respondents from all three countries felt more strongly towards reciprocal altruism and social justice and less towards monetary rewards. Regarding privacy concerns, however, the surveys presented discrepancies among these countries, indicating stronger cross-national influences on sharing concerns than on sharing motives. Cross-national differences in privacy concerns and their relationship with motives were nuanced and context-dependent.