[Hallicrafters] SX-28 selectivity fault?

[jeff]

Hi,
Im in the process of fixing the faults in an SX-28 receiver that has been re-built by the previous owner. 
One last thing Im not sure about is the operation of the selectivity switch. As Ive never owned an SX-28 before, I need some advice as to whether the selectivity switch is working normally or is faulty.

On 'broad IF' receiving a strong medium wave station, the meter indicates over S9. When the switch is then set to IF Medium, the S reading drops about 3 S points. When then switched to IF Sharp, drops another 2 points. The audio sounds like the bandwidth is reducing as expected, but am unsure about the drops in signal strength reading. Probably faulty, but thought Id confirm.
Any advice appreciated,
regards,
JEFF
ZL3JK
New Zealand.