I have a 2 story with ductwork and plenum under the slab. The plenum has rotted on the bottom and about 1/2 way up the sides so the air is blowing into the dirt then the ducts. I know this is a problem but am getting conflicting opinions about whether to repair or replace. Repair is less $$ of course but that's not as important as getting it done correctly. Is repair a good way to go?