I've got an older deore lx front derailleur for a mountain triple crankset. It wasn't shifting properly, and it seems that it's sticking and not returning back to a neutral position when I shift it. I've tried loosening both limit screws with no change in behavior. I took it off the bike and tried to move the derailler as if I was shifting, but doing that moves the cage, but it doesn't try to return to the original position.
I'd like to soak the derailleur in a cleaning solvent (such as kerosene or paint thinner) to remove any gunk that may have built up on inner surfaces. Should I worry about the solvent damaging parts? Is there anything else to try to revive the stuck derailleur?