there is no Mrs. Lankowitz. Maria Lankowitz is a placename. :)
for Styria you need a placename also to find the records you need in the parish-church. for this you can ask at diocesan-archive Graz, but without a placename they can do no research. so do you know WHERE he was born?

austrian phonebook has 63 hits for Rucker in Styria/Steiermark in 10 districts. so you know why you need a placename to find the correct entry in the church-book.
Graz (Stadt) (22)
Graz-Umgebung (16)
Deutschlandsberg (8)
Voitsberg (6)
Murtal, Judenburg / Knittelfeld (3)
Murau (3)
Leibnitz / Bad Radkersburg (2)
Feldbach / Fürstenfeld (1)
Liezen (1)
Bruck an der Mur (1)
http://www.herold.at/telefonbuch/steiermark/rucker/

Steiermark: http://de.wikipedia.org/wiki/Steiermark
Styria: http://en.wikipedia.org/wiki/Steiermark