Homeowners' Insurance - When to file a claim vs. pay out of pocket

[statsgeek]

Wise forum, I need a crash course in home insurance. 

Our roof is due.  It's at least 20 years old and we're seeing the beginning of a leak.  The roofing company is strongly encouraging us to file an insurance claim since there is visible hail damage (although it's not clear the leak came from the hail damage). 

I checked our policy - we have a $5000 deductible and actual cash value (rather than replacement value) coverage. The way I calculated it, IF the expected life span of the roof is 30 years (and I doubt it's that long), the insurance would calculate the actual cash value to be no more than our deductible. 

Depreciation = age/lifespan * replacement cost = 20/30(15,000) = 10,000
ACV = replacement cost - depreciation = 15,000-10,000 = 5,000. 

Am I understanding this correctly?  It's not going to do us any good to file the claim, and may harm us if the claim is on our record and something unexpected does happen?