I can't answer the question for you about whether FLUSH works for local and not network drives, but I understand that it forces the data to be written to the disk. Hopefully, someone will enlighten both of us on this issue.
After we exchanged the last notes, we both received the note from Thomas Martin with the OppLock settings on the NT Server. Presently the customer is checking out the effects this setting will have on the rest of its network (email and other systems) before they will change this setting. I will let you know what happens.
Adam J Skowronski