Lincoln Center always has a cancellation line. They allow members to return tickets up to 72 hours prior to a performance, and they often hold back house seats and seats for exchanges, so seats are almost always being released day-of. If you want to see MFL or Admissions, I'd suggest going to be box office the day you want to go and ask if they have anything available or if they're doing a cancellation line. Either way, you're likely to get in.