Hi Garth , I also have a model T413 12 string. Bought mine in Japan 1972. The sound is still great with a lot of depth. I had just got it out tonight to play it after sitting 2 and a half years, the thing was still perfectly in tune. I had put new Elixer light strings on and played it awhile and then parked it. As mentioned before I had purchased it brand new, the catch is that I was in the Navy and I had it in tow during my 10 years going all around the world through all kind of harsh conditions and yet here I am now still playing it and it still sounds great. Quite a testament to an inexpensive guitar of that period. I found tuning it down to D may have helped its longevity. After all of this I still know very little about Kasuga Guitars but am very pleased with this particular guitar. I just need to play it more so my fingers can hang. Best wishes and good luck in all your quest.
            With warm regards, Mark