How hard is it to rebuild a master cylinder?

[odog]

Just like the title says, I can get a rebuild kit for a master cylinder from a 67 3/4 truck with front and rear drums for $8. Is it worth doing, or is it a big pain and not really worth the trouble.

I have said master cylinder on my 69 and basically no breaks. The pedal goes to the floor and has little resistance. I have to add fluid about once a month, I have blead the system and cant find any leaks. The only thing I havnt tried is replacing the master cylinder.