The wooden seats were standard on the PT-13D/N2S-5, though they may have started to show up earlier, and the serial number and part number were usually painted on the bottom of the seats, underneath. Usually they were a dark green, almost a forest green. I have a couple that need some major repairs too. Probably the best place to look for someone who can fix them is over on the SRA's bulletin board (
http://www.stearman.net) as there was a guy awhile ago that was making new wooden shells from scratch ($2500/ea seems to ring a bell) If you find someone let me know. This is an original one before I overhauled it. The color is a little faded but still pretty close.