when i worked at the dealership, if we saw carpet, nuts, fiberglass, etc. in an hvac system, we ALWAYS replaced the parts. those little guys love to chew on just about anything! i'd hate to see you spend the time to clean it up, reuse it then find out it has a leak on your new carpet in the interior
plus..... well....... it's old. replace all the heater/ A/C components in my opinion. thats my plan anyway...