u/No_Acanthisitta1249

This stain (no before picture) has been on the ceiling of my garage since we moved in a year ago. I should've checked it before but brushed it off. I noticed a slit here and poke my finger through it and noticed multiple holes in the dry walI. It's not damped but I do few small wet spots. never noticed how bad it's gotten. I know I have water damage. The garage is above our bedroom and master bath. My question is, what's the next step to pin point the leak? Should I cut the dry wall and see what's underneath or should I just call a plumber to do it? Any help would be much appreciated thanks