Farm out the blower motor rebuild and do the rest yourself with the gasket kit from the 71TA (DMT). You can have the part number stamps made, or buy them I think.
I have bought two used heater boxes online and both showed up damaged from shipping monkeys. Found one at a local parts hoarder guy's place and bought it in person.
If yours is still ok . . . you should be able to clean it up and redo yourself . . . as said above, the gasket kit from DMT (71TA) is absolutely perfect ! I did my own on my Sport Satellite - AC car . . . cleaned up great, even the stamped part numbers were still there and very visible !
Good luck
Mark