Welcome to AK,
You may get a better response to your question if you post it in the TAPE section of the Audiokarma Audio Forums.
HiFiEngine.com has numerous operating and service manuals, however the only ones available for Sankyo decks are their models STD-1700 and STD-1800. But I don't think there's any similarities to your 1410.
Also, you might try posting your question on the TapeHeads.net forums.