Metal Roof Repair in WINTER what products are good for cold temps

I have a commercial building with a 10 year old metal roof the previous owner had put on. I am doing some remodeling so the interior of the roof is visible. I assume the metal roof was put on over another older tar roof of some sort. The building really is 3 walls and the 4th is shared with the building next door. I have had trouble with leaks along the corner where we meet up with the neighbors down the wall. I think the flashing where my building meets theres is leaking. Is it best to call a roofer who does metal roofs and put on another layer - fix whats here. Or is there some sort of sealer I can put on in cold weather? I had thought I had stopped the leak by caulking every screw seam whatever for 20 foot from the leak. But first Ice storm and its back. The trouble seems to be it could leak - move down the "under roof" and then leak somewhere else. Very troublesome for finding the source. So any advice on finding the source or products to use to seal it - please let me know, I can also send pictures if it would help.
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