My wife has a Takamine 12-string from the 'logo-copy' era. Martin sued Takamine to change their logo as it was made to look exactly like the famed C.F. Martin. Kasuga's were very much in the same mode in terms of quality. My considered advice would be to spend the money and improve the playability of your 12-string. And you're right re the cost of a new instrument of comparable quality. One would spend thousands in todays market...that is unless one finds another Kasuga at a pawnshop, flea market or yardsale. They're among the best of the Pac-Rim copies.

Alvarez-Yairi, Takamine, Aria, etc. all made great instruments that superceded the quality of the American name-brand instruments of the same era.