I have this same Starbucks Barista machine and have fixed the leaking steam wand problem twice over the ten years that my machine has been operating. At the time that I had my problems (3 and 7 years ago), Starbucks used to provide over-the-phone assistance (even beyond the warranty period) to adjust the machine. You would open up the machine from the back and they would wait on the line to tell you what to do next. There were no parts needed, just an adjustment to the steam wand valve. Unfortunately, Starbucks does not provide this service any longer, and I don't remember exactly what we did... Sorry!
I am now faced with a boiler problem on my machine. Perhaps it is time to get a new one!
Good luck!