I've worked at a company for about a year and most of the stuff I support is custom. At this point in time I'm pretty comfortable supporting most of our software to external customers. However, occasionally I have to support something that I still have no experience with. What I'm supposed to do according to my boss is speak with a specific more senior employee. A lot of this software he wrote himself so he knows all of the little quirks.
The problem arises when I ask him for help and he is too busy. Typically, I will mention it in the morning and again after lunch. His response is usually "yeah, I'll be right there" or "as soon as I'm done with X". My latest issue has been dragging on for three days because he keeps putting me off. Now I have 2-3 issues stacking up that I need his help with. My gut says to go to our boss so he can tell him to re-prioritize and help me. However, I don't want to be seen as "telling" on him, especially since he's a nice guy just really busy.