I was having alot of failures with slave in my m5ord. The seal gets eaten up from all the mud/dirt etc..
I took mine out and got some screen mesh ( like from Lowe's for house windows). I made a few plates, drilled a few holes in bell housing and covered the openings with the mesh to keep the larger nasty's out. I was replacing a slave a year, now they are easily lasting twice as long since doing this.
Also make sure the fluid itself is good and clean.