Question about Duncan pedal? (not DIY pedal but I want to fix it myself)

[veronica 1965]

I have a Seymour Duncan Univibe pedal, probably about fifteen years old, that I haven't been able to use for about ten of those years. When I add it to the chain, my guitar's volume drops significantly (say from 10db to about . In addition, the sound is severely muffled; the treble is really cut. It sounds like i have my guitar's volume on about 5 and tone cut altogether. Can anyone explain why this might be happening or what types of parts might be needed to repair it? Thanks very much!