I concur, Roland: I have one picture of the following production batch which Stkz was "RU+Gx": Bf 109 G-6 W.Nr. 162 601 "RU+GS":
www.flickr.com/photos/28092068@N03/5293931987
According to the LEMB STKZ, Bf 109 G-6 W.Nr. 162 577 had "RU+FU" as a Stkz. The preceding batch in the "RU+Ex" is completely documented from W.Nr 162 531 "RU+EA" up to W.Nr. 162 556 "RU+EZ"; we would have indeed "RU+FO" for 162571.
Cheers
Marc