If you go to Ebay and click on HOME AUDIO and then type in MARANTZ, scroll thru the pages as there is a person selling a replacement gear that is orange for various players with this transport. Your Theta data basic is mentioned that this gear will fit. This is what the site says;
Newly made in Japan and better material than the China made one.
This is a brand new Tray Gear wheel For Philips CDM9 , CDM9 PRO Tray.CDM9 usually used in CD-players like Meridian, Marantz, rotel, Philips, PS Audio(Lambda, Lambda II), Rotel, Arcam, Theta(data basic,data basic II) .........
Philips CD-930 CD-931 CD-950 CD-951 LHH100 LHH200, Marantz , Aura CD50 CD100