Brake system info needed

1997 Grand Voyager developed a leak in what appears to be an equalization block on rear drivers side just before the wheel. The block is leaking under one of the rubber dust covers when pressure is applied to brake. Is there a rebuild kit for this or just replace the block?

Thanks CC

It's called a proportioning valve. My '98 had the same problem. http://www.automotiveforums.com/vbulletin/showthread.php?t=505423&highlight=proportioning+valve
As the other posters said, make sure it's not a leaky line. I got a replacement from a dealer for $55. Was hard to find as a couple of dealers said that this is a common problem. Hope this helps.