Nautilus P1 has leaking connections

where exactly is it leaking, throught the threads or from the hose side?  you said you use pex conectors, are the hoses actual pex, or the flexible garden hose stuff they like to use in rv's ?  if it is the latter see if you can replace it with real pex.  if not, you have to get proper fasteners for it, pex clamps on non-pex lines is a very bad practice and just prone to leakes, but the rv manufactures do it because it is fast and cheep, and thats what they are all about.