I sent an e-mail to Glasfaser, as I also have a T59D. Here is the response I received:
____________________
Hello,

from us the T 59 Kestrel is not affected.
Our company is not the TC holder and all other infos you
can find on our homepage www.streifly.de

Best regards
H. Streifeneder
____________________

Begs the question: who is the TC holder for Slingsby Kestrels?