If I remeber correctly, there is a rubber bush a steel sleeve then a nylon bush under the contact ring. I think the contact ring is always hot, so any grd will cause the horn to blow. I had the same problem (sort of) a while back whem my GT6 was assembled, and it tuned out to be the wire that connects the contact ring. There was a portion that had no insulation on it, so when I pushed hard on the wheel the wire moved and shorted to ground. I solved the problem by taking the while car apart and never putting it back together....
Actually I'm doing a frame off on it, so it really is in pieces, but it was the short in the wire.
Let me know if that hope that helps.
If not I can take a look at my steering wheel horn assembly, it's in storage, but it shouldn't be too hard to find.
Mikey