There's the "Stream type and A/V Interleave" window which may help. Check with a file that has a known delay and see if you can figure out any pattern or something like that.

okay I found the window! For one file that has a 1000 ms delay, under I/L it says 1 vid frame (42 ms) NG=1008 Split: Yes. On another file with no delay it says 1 vid frame (42 ms), p=480 Split: No. So I wonder if this means something? Like NG = delay in ms?

I might be wrong but it seems NG=negative, and p=positive

that might make some sense, because vdub by default preloads audio by 500 ms, which might explain why the file with +480 ms delay plays in sync...