I sent the message below privately, but thought I would mention to the list that I keep the message as brief as possible, and avoid all cataloging jargon as much as possible. My usage "to distinguish you from the others" is deliberately calculated to stroke the author's ego.

Jack Hall
Music Cataloger
Metadata and Bibliographic Services
University of Houston Libraries
Houston, TX 77204-2000
A Carnegie-designated Tier One public research university
phone: 713 743 9687
fax: 713 743 9748
email: [log in to unmask]

I don't have a template I use but my emails read pretty much like this:

Subject: Cataloging your book

Please pardon my intrusion. I am cataloging your book with title: .... Publisher, date, for the University of Houston Libraries. I find more than one author with the name X  Y and would like to distinguish you from the others in library catalogs. A convenient way to do this is to use your birth date, if you are willing to give me this information. Other forenames or initials you use besides X could also be helpful.

Thank you,

Sometimes I add something like: Are you also the author of this title/these titles ...  (if I find other titles that I think might be by the author in question) I find I am often successful and the authors are surprisingly willing to give me their birth dates.