That sounds like the internal diaphragm has cracked.
You can't repair the old Vacuum unit without a lot of specialized equipment, so you'll probably need to replace it. It MAY be a dealer item. Check with a local auto parts retailer to see if they can get one for you.
On 3.0L and 4.0L engines, the PCV valve is mounted in the valve cover near the brake booster. - Haynes Repair Manual #36071, 1993-2005 Ford Ranger Pick-ups, all models.
If you are wondering whether or not brake booster repair is something easily done by an amateur because you want to fix it yourself, then the answer would be no. Take it in to get it fixed.
repair manual fora front differential on a 2001 ford ranger edge
autozone.com has online repair manuals
Look up 2000 Ford Ranger in the RockAuto.com parts catalog and find repair manuals under Literature. The 2000 Ranger repair manual is on DVD - ROM for about $14.
The only permanent repair is to replace the gasket with a new one.
Get a new one .
just checked my ranger repair manual, this repair has some procedures that have to followed, would recommend purchasing the Haynes repair manual for that model year it covers both 4&6 cylinder engines
The slave cylinder on a 1988 Ranger can not be repaired. The cylinder will have to be replaced, then the system bled.
Take it to a repair shop.
Get a repair manual from your local auto zone its hard to explain where it is, on my 4.0L Ranger its on the bottom left .
You need to find and repair the vacuum leak.