So my guess was correct

STC used to stand for Suzo Trading Company, but now it's used as Suzo Technical Components. Rotterdam (in The Netherlands, for those who do not know

)was their home from the start, but they've moved to a place outside of Rotterdam now.
The sliding is probably caused by a missing E-clip ? If that's the only thing, you should be able to get one at any hardware store. However, the handle looks very shiny, and normaly (new state) they are matt. So it has been used quite a lot.
I had two Suzo 500 sticks on the Jamma cab I bought. The left one (player 1) was obviously used the most, there was some room to move the stick which shouldn't be there. The other one was as new though. Those sticks should cost around the