You have a puzzling inquiry here.
I don't have a 123 but I would suspect, that the Air Deflector was designed for air to be diverted down and across the Hydro Unit.
On a personal note, being a HVAC/R Tech, I don't see any difference between the air going straight back vs going down. The objective is to have air to cool the Hydro Unit.
I looked at the Online Parts Lookup as well as the old paper Parts Manual and I could not find that deflector.