ok well I fell that it is best to put new seals in because i have reused seals and they did not hold up. The result was i wrecked a cosmo iron. I have however heard a tale of a really smart rotor head in my area that uses one st of o ring to do 2 rebild. you just take the front and rear irons off then leave the housing in place so you only have to use two sets instead of four. then use the other two for another rebuild the trick is not letting the middle section seperate. well thats all i got hope it helps.