Ah, I wouldn't swap that fear to dread just yet. We've sold hundreds of sets and had 1 complaint about a single part fitment and 5 complaints about leaks, it's pretty easy to have an issue with o-rings and assembly if one isn't well versed in joint makeup -and most are not. Take your time, make sure everything is very clean, inspect surfaces of mating parts to ensure there are no defects -particularly those that cross seal barriers- and you're going to be just fine.
Chris
Chris