As Grainger said that resistor in the input selector is ripe for replacement - I am bunging some Shinko tantalums in there to see what happens :-)
Now I am going to disagree with Grainger the volume control(s) is also fresh for fiddling.
However I wouldn't recommend just changing resistors here.
What you need to do is to change it over to a proper ladder attenuator.
This requires new switches and a *lot* of soldering - basically you are now dealing with at least twice the quantity of resistors which also at least doubles the cost of your boutique components!
But it is worth it as a ladder gives you a fixed input impedance (which things like valve based phonostages prefer).
Hopefully my new attenuator will arrive before the fat bloke goes charging around interfering with childeren...