The Telefix was an aftermarket stabilizer and there continue to be decent copies of it. The reviews for them have been favorable i.e., they make somewhat of an improvement, but a stabilizer is unlikely to correct the degree of wobble that is described in your post.
What you can do right now is adjust the steering head bearing. With the Brick's front wheel centered and off the ground, the fork should slowly and smoothly turn to full lock in either direction when the handlebar is released and slightly nudged. If it swings rapidly or not at all, the bearing either needs adjustment or replacement. Complete instruction can be found in the BMW K75/K100 workshop manual downloadable from this site.
If the handlebar can be moved fore and aft slightly when pushing or pulling on it when the wheels are off the ground, the bearings are worn. Bearing condition and incorrect adjustment can cause wobble when the tires contact pavement irregularities at speed.
Check the fork tube alignment by laying a pane of glass that is as wide as the fork tubes' horizontal outside dimension and sufficiently long enough to cover much of the tubes' clear length. Both tubes should make full contact with it. If they don't, the fork has stiction that affects the freedom of the fork tube's compression and rebound. That will also cause wobbling and weaving. The tubes must be in the same plane for the suspension to work well.
