Use whatever brand of JASO FD oil only. Never Stihl Ultra (JASO FB) even if they give it to you for free. Germany gets the good stihl oil, we get the crap stuff.
You can use techron without harm at the proper dosage. It may not do what you expect. A carburetor screen can still get clogged. Varnish from the stihl ultra will take time to clean off if it has built up.