The best way of thinking about the etiquette of masonic correspondence is peer to peer or within groups with someone in the group being about to write outside it. Members can informally write to members. Only GSec should write to other GSecs (or their reps). GM to GM. WM to WM etc. A big factor is once it is outside your jurisdiction, the ideal is GSec to GSec for correspondence.... and there is a real difference between formal and informal correspondance. I would drop an email to a WMGM anywhere I knew if writing informally, officially, I would get our GSec to write to his GSec or authorise me to do so...
The logic which is being followed was - member write to his Sec. His Sec writes to his GSec, His GSec write to other Jurisdictions GSec. We can all immediatly see the potential problems..
@MarkR is correct. The public often writes to GLs, so don't write to them as a Freemason, write to them as a member of the public, but do mention in somewhere that you are a Freemason.
Better to beg forgiveness than ask for permission sometimes... because you have seen where that has (not) go you
@Mike Mendelson
One thing, they will have a policy. Usually, the member need to be deceased, or deceased for a certain time before they will release records (also remembering they are also affected by any privacy laws).
Also note, I am aware we have members over 100, so age alone won't see the record released unless of an impossible age.
Give as much detail as possible, full name (including middle names), DOB, location.. and sometimes profession can help. Hopefully your relative is not called John Smith !