A/C Retrofit Kit

My 91 Olds Cutlass Ciera had a leak in the evaporator & hasn't been converted to R134 yet. I've had the system evacuated by a local shop & picked up a new evaporator & accumulator, these are easy enough to do, & then I'll take it in to have the recharge done. The A/C retrofit kit to convert to R134 is something I haven't done yet. The new high & low pressure fittings are straight forward, but is it necessary to put in all of the new O-rings? Any info would be appreciated.