i will have to admit, the one problem i ahd with Z1 with cores on my injectors was resolved by Russell since he clearly admitted it was Z1's fault for not listing it properly on their site. So it took a phone call or two to get my core back but it was painless (cept for that night i had to wait to call them back in the morning but russell called me first :)) and since then they have updated their website to reflect upon the requirements for core. i do forsee myself doing more business with z1 in the future but they are not my ONLY source for parts.