The first thing you can try is turning down the VR for the squelch (VR102) and see if this alters it enough.

If not then replace the resistor that is in series with the VR (it is located close to the VR on the left side towards the rear of the set) with a 47 K Ohm resistor.

After this mod has been done you will need to turn the manual squelch up higher than previously required to mute the signal levels.

The auto squelch should now allow weaker signals through.