Looking at a 1987 Wrangler that the seller says neeeds a clutch slave cylinder. He says that someone tried to fix it. They put Hydralic oil in instead of Hydralic fluid. Can the system be drained and flushed or do you need to just replace the slave cylinder? Thanks

most likely the slave cyl is leaking,They were probably hoping the thicker fluid would help/slow it down.Very common on the 4 cyl engines to have leaky slaves.I think it's because of all the shifting you need to do with the 4 banger.Expect to remove the trans and replace it.

I've got an 88 Wrangler. These jeeps in this year did not run an external slave cylinder. They ran a hydraulic throw out bearing, so you have to pull the trans to replace it. You can try draining the oil and flushing it out with brake fluid to see if it helps, but if it's leaking, the trans has to be dropped.