You may need to get a duct camera. Used by professionals who do duct work and cleaning.
Or you could get one that plumbers use or one that chimney repair people use to inspect chimneys for cracks.
You need something that gives you video access to find out where the damage is and what needs to be repaired.
Good luck. It does not sound like it will be easy.
2017 F450 Lariat CC LB 6.7 Shadow Black/Magnetic, ChromePkg.,bedliner, Retrax,TS3 Hitch,55 gal.aux. tank, 200 psi air system
2016 Mobile Suites 38RSSA, induction cooktop, solar, (4) 6 volt, full body paint, 17.5" Tires, 3" riser