Along with what everyone else said....
I'd suggest a small investigation first. Pull the drums, got to do it anyway, and check for fresh fluid....and check all along the line. You may have a small pin hole in a line that is rusting from the inside out.
In my neck of the wood finding just the cups is almost impossible unless you have an old supply parts house in your area. Most will sell only kits but seeing how they are not expensive "any" kit would work as long as the cups are the correct size. Most cups will have the size on the inside of the cup.
