bad slave cylinder in '96 f150. what else to change?

Your clutch was at the end of it's life anyway, the reason these style slaves fail is because of the pressure plate, over time, heat will cause the diagram spring to increase it's tension until it blows the seal in the plastic slave.

You will need to put a Slave cylinder, a "Clutch Kit" into it, and have the Flywheel resurfaced.

(as the other poster mentioned) be careful on the quick disconnect at the slave, when trying to release it make sure the nylon release ring is pushed all the way in and at the same time pull straight out to disconnect it.

NOTE: You didn't mention what engine option you have, 4.9L, 5.0L or the 5.8L, but be sure to measure the clutch, because you could have an 10" OR an 11" clutch in this application.

my advice is take Robert M. with a pinch of salt.

Brake/Clutch fluid should be changed periodically, but as long as you use the right stuff i.e. DOT4 in a system designed for DOT4, you shouldn't have any problems.

If youre taking the box out to do the slave cylinder, you might as well do the clutch and release bearing (although i assume you have a concentric one which is why its inside the box?) while you're at it. Obviously check the clutch and flywheel and stuff to see what state its in, but i would probably do the clutch while i'm there. So you're looking at Clutch, Clutch Cover and Release bearing or Concentric Bearing/Slave Cylinder (whatever you wanna call it. Possible flywheel if its all uneven and/or scored etc.

Go ahead and change out the slave cylinder, and be careful putting in the fluid line. Have a friend come over and fill the reservoir, and bleed off any air left in the cylinder. Push slightly on the clutch pedal, while bleeding off the air. You don't want the pedal to be "soft". Open and close the bleed screw just enough to let the air out before pulling back on the pedal.

You're done!

since you asked what else, id look into both the clutch master and slave cylinders. the slave is in the bell housing, mounted directly in place around the input shaft.

You are makingre a BIG mistake, MAYBE ! The nnmber one cause of a LEAK is OLD BAD ROTTEN clutch and brake FLUID! the manual will tell you to change the BRAKE fluid every 3-4 years! it absorbs MOISTURE fromt the air, SPOILS gets TOXIC and begins to shrivel seals in the brake or clutch system ONLY USE FRESH GENUINE FORD brake fluid, and POWER FLUSH all old fluids OUT of the system Do this with CLUTCH and with BRAKES! chances are VERY GOOD that your SLAVE seals will repair themselves once the SLUDGE in the system is removed. You do NOT really need NEW CLUTCH parts, MAYBE! FIRST STEP IS THE fluid change AND THEN LOOK DEEPER. trust me! good luck!!

while you evaluate it extremely is type new did you replace the throw out bearing,preesure plate ,and snatch besides as grind the flywheel and replace the enter bearing? if specific to all. is there any adjustment left to the sleeve or fork adjustment? placed it nutrel,word parking brake, initiate it up and see in case you may get in first equipment. its nicely worth a attempt.