My mother, my SO and I have all experienced leaks in the past year. Mom’s was due to an ice dam, mine was due to the plastic covering coming loose around a bathroom vent pipe, and the SO’s was due to a broken roof tile allowing water to gather under the flashing at the edge of the garage roof and the adjacent part of the house.
In the case of the SO’s house, I had ~5 roofers come over and take a look. They all had differing opinions on the cause. One of the five fixed the problem in a matter of minutes. It was much cheaper than having the shingling replaced (as one suggested) or going through the insurance company.
My advice? Get multiple opinions from those in the field first. It’s time-consuming, but it can pay off in the long run.