Trying to fix a hissing MXR Stereo Chorus

[pedaljunkie]

Has anyone ever teched an old yellow MXR Stereo Chorus (corded.. no battery or 9V jack)?  This thing, once engaged, is hissing like hell out of both R and L jacks but sounds pretty awesome otherwise.   It was given to me because it doesn't "work" and the person didn't want to deal with it anymore.  I am posting prelim pics of the box and its guts.  I also recorded a sample of the problem sounds.  (not sure how to post the sound file tho)  I really would like to fix and keep this old beauty.  I'm going to get a bit more under the hood tonight and this weekend.  No hissing when bypassed, BTW. 

Thanks in advance as always!   

[artifus]

nature of the beast i fear. good luck.

[Fender3D]

Hiss is a "feature" in most older pedals...
And many players will perceive the lack of hiss as a lack of treble or higher frequencies...
The dual dip switch will change gain for a better operating environment when using "line" or "guitar" signal level, check if you get a better ratio with a different setting, first. (you'll have unity gain when all on or all off, though)
Otherwise, you may improve S/N ratio with better op amps than 4558 or 1458 expecially for U1, U5 (4558) and U4 (1458) since they add gain to signal, try with TL072 or 5532, or dual OPAs.
Carbon resistors are another noise source also...
I guess almost the whole left side (in your pictures), should be replaced... 

Good luck