Rear brake cylinders: repair or replace?

["gregs672liter@netzero.net" <gregs672liter@netzero.net>]

Greetings list, I believe I have a slight leak in a rear brake cylinder (have 
to look,, but the fluid is down slightly in the master).  What has been the 
success on rebuilding the rear cylinders?  Are kits available, or should I go 
ahead and just get new cylinder(s)?  Thanks.
Greg Burrows