upon arrival, it seems like its in part due to the thin walled seat stays. i know of others builders using the same stays with good results, never the less...lesson learned. thicker stays next time.
i decided to replace it with some comotion disc drops from pacenti cycles. they are designed for tandems and mountain frames. they are so burly, its not even funny.
i thought that the tab for the seat stay would be long enough when i cut off the damaged portion of the stay, but no dice. i had to do an internal sleeve and extend the tube to meet the tab. i then replaced the brace from the seatstay to chainstay. this may not be necessary with the disc tab being part of the dropouts and the things being so stout , but i did it anyway for good measure. plus its adds to the strengh of the internal gussetting. all brazing was done with brass and i left the ends of the stays square in order to have as much bulk at the joints as possible.