I've used white distilled vinegar with success in removing old conductors that were stuck in conduits (assuming from poorly poured sealoffs). It takes some time and effort.
Things I have done is to (after breaking out/removing chico from the sealoff, filling the conduit with vinegar and leaving it overnight.
Then try to free the conductors one at a time.
Most of the time the 12's and 14's would come out but the 16's and 18's would have problems.
Sometimes the wires break off down in the conduit. Once I get all of the conductors out that I'm able (assuming a couple are broken) I would shove a fish tape down the conduit, the tape had an offset bent on the end (hook is cut off), when I hit the obstruction (the 90 with chico?) I would cut the fish tape off and put it in a drill. Then run the tape up and down with the drill turned on.
I would always use a small pulling becket on the conductors when pulling in the new ones with the idea that it might offer some protection to the conductors.
Hint, DO NOT BLOW FROM OUTSIDE TO INSIDE. I did that once because we didn't have enough hose to run to the back room (using a tow behind air compressor that you typically use with jackhappers). What an effn mess. Took me 4 hours to clean up that back room SMH.
I only remember 3 jobs that I couldn't get new wires in old conduits.
