Seanf,
Cover would be cost of new machine.
If all bearings seated & everything detailed, like high spots on rotor end faces, discharge end face, clearance should be correct as it was from factory.
If correction required, precision lathe work on cover carried out.
Must be perfectly parallel to each other.
Face machined depends on if clearance to big or small.

All these machines are about cleaning & detail for reliable operation.
Also check & double check everything ( Tycho indicates this in video).
If checks not carried out it goes pear shaped pretty quickly.