I'm so glad you asked for my advice. You sure are in a difficult situation with the problem concerning (name). I was in a similar situation one time and understand exactly how you are feeling right now. The problem is a difficult one, but one I'm sure you can resolve...
Dear (recipient's name),
I'm so glad you asked for my advice. You sure are in a difficult situation with the problem concerning (name). I was in a similar situation one time and understand exactly how you are feeling right now. The problem is a difficult one, but one I'm sure you can resolve without any conflict.
The first thing you should do is address the problem with the entire group. This way you aren't singling out any one individual. If you single out (name), he's bound to become defensive and that can only hinder your progress. If the problem continues after the group discussion, speak to (name) privately and remind him of what you discussed in the group meeting. This is a nice alternative short of filing a formal grievance process. It also covers all your bases should you need to take further action. If the problem continues, you will need to file a formal report. By this point in time, you can rest assured that you've done everything you could to minimize confrontation.
This is such a difficult situation, but I know you'll be able to solve it without any confrontation. I'm confident you will be fair and open-minded with (name). If you need anything else, I'm always here for you.
Sincerely,
(your name)