If the OP came in with his reg showing this leak I would do exactly what mattboy, ScubaInChicago and DA have mentioned. I have seen examples of both a loose DIN fitting and damaged o-ring where the fitting meets the body. One thing you do learn both in the reg seminars (and yes, some are better than others) and OTJ training is to troubleshoot. If this reg was presented to me I would not feel I had done my job unless I had checked the internal o-rings and the DIN/body connection, as well as the correct torque. If I had to change an o-ring and maybe do a bit of thread cleaning might I charge a bit for this? Possibly. $50? Almost certainly not, unless I had to do a complete rebuild.
At least at the conclusion I would feel confident that the reg was working properly and that the OP wouldn't be returning with the same issue.
At least at the conclusion I would feel confident that the reg was working properly and that the OP wouldn't be returning with the same issue.