, you'll generally want to look for .srt files that match the "VXT" or "BluRay" encode timing.
For this specific release, you can find compatible SRT (SubRip) or ASS files on several reputable subtitle repositories:
One of the biggest controversies regarding Oldboy involves the English subtitles. The original Tartan Video DVD release had poetic, slightly liberal translations. Later streaming versions (Amazon/Netflix) used a more literal, dry translation that ruined the emotional impact of the final twist.
: Often has high-quality, community-vetted subtitles. Look for entries labeled "BluRay" or "Remastered" for the 2003 version.