This paper presents aspects of eight advanced Korean EFL speakers' acquisition of English unaccusative verbs over a period of five years. It examines how three factors−L1 morphology, pragmatic causation, and animacy−have affected their English unaccusative verb grammar during that time. A forced-elicitation grammaticality judgment task was performed three times over this period. It showed that L1 morphology was the most persistent among these factors. The results are compared with Chung (2014), a cross-sectional study, where the same method was used. The findings reveal that the Korean EFL subjects' overpassivization of English unaccusatives is not fossilized, which differs from the findings of Han (2006), who examined two Chinese native learners of English. It also indicates that instruction can play an important role in long-term L2 learning.