Congratulations,
Your grey with yellow buttons SEIKO RC 1000 must have been a newest (e.g. limited edition - even a prototype) variant of the regular black/red buttons RC 1000( thus the 400A, instead of a 4000 SN) and I am quite sure that is very rare (never seen one with a grey case, not to mention with the yellow buttons :).
Hope that You are aware about the possibility to built Your own interface for some serial interfaces of more modern PCs and to use the shareware "Seiko Tools" software to "play" with the watch...:)
On the other hand and unfortunately, while it was very handy for schedule's programming, it will not allow any use of BASIC language programming nor of the binary uploaded games, as the DATA 2000 (UW01-0020) - UC 2000 (UW01-0010) - MEMO Diary series (e.g. UW02 calibres) etc already allowed in 1983-1984 ...
Best regards,