Had over 200PPm CO spillage on a Heat N Glo GDV 5000. It had the silicone gasket, most of which was missing, so ordered a new glass with rope type gasket.
Installed new glass and now have 5-10PPM spillage around one side only.
Pulled and checked glass, gasket, and insert for issues - nothing obvious, no bent metal, missing gasket, old gasket material stuck on unit. Wing nuts are tight and I tried with and without rubber on brackets.