Tintin,
It's not just the pastors. No member of standing in the LCMS can be a Mason. They take a very hard line stance. Before becoming a member of the LCMS a person wanting to become a member will affirm they do NOT belong to the Masons or other of those types of groups. (At least that has been in any LCMS I have attended so far)
PS (The guy asking the questions is not the pastor)