I have a 1999 GMC K2500 4x4 crew cab w/ 7.4 liter with 67,000 miles. It has developed a leak on the power steering system. The leak is on a gold colored-cylinder shaped device that is mounted on the firewall and has p.S. Hoses running to it. I cant find any info on what this " cylinder" is or what it does. Thanks in advance.