I own a morley pro series wah... made in 1998. It's only function is Wah. So one day, it fried. It turns out that only one side of the opamp (TL072, I think) was bad. So I got the schematic on their site and it turns out that if you bypass that side of the opamp, then you get added functionality: volume control. So now I have a Wah/Volume pedal. Of course, I had to add a few components, like another photo-resistor + led. Their PCB layout is really awesome too! They used the same board layout for the Wah, The Distortion/Wah and the Volume/Wah pedals. So I can see where all the missing comonents (and their names, like C1, C2, TL072 etc) would be, complete with solder pads and mounting holes.
So, used morley pedals are worth buying, even if they are broken... they are easy to fix.