Performed diagnostic. Tstat properly calls for heat cycle. Found upstairs damper motor stuck open and wires disconnected. Hooked up wires and zoning worked properly, dampers have potential to fail again in future. Found blower motor leaking excessive oil at bottom seal and run capacitor testing below spec. Hot surface igniter shows wear but ohms within spec. Performed safety inspection, no gas leaks, checked electrical connections. Inspected heat exchanger, multiple areas of concern, behind high limit switch on lower eyelid found metal fatigue and breach. Advised home owner not to run furnace due to potential safety concern. System is operational. No model or serial number on furnace at all, could not order new heat exchanger, suggest looking into replacement options.