Well, there's definitely something additional wrong with this gun that I don't think is going to be fixed with a seal kit. I've got an NR2000 as well as this SJ 2000 RP - both are identical with exception of one being an RP and one being a standard HVLP. One by one I stripped the parts to isolate where the leak is actually coming from, and I found it.
I figured this thing is nothing more than a pneumatic tools, so I started getting a little creative in trying to trace down the leak. On the gun that works and seals right, I aired up the gun, set a low PSI (about 20), and while it was aired up, I unscrewed the fan control knob, and removed the fan control assembly, basically exposing a hole in the side of the tool where that control knob/assembly would sit. While it was aired up, it still held pressure perfectly. Not a single leak... Now, with the gun that DOES leak... I did the same thing, and found that air was leaking into the trigger cavity (the area in front of that plastic piston/cup seal) via a small hole directly underneath the trigger rod. It's worth mentioning that the hole exists on both guns, but it's
only leaking on the RP.
After seeing that, I was thoroughly confused, so I brought up an airflow diagram of the SJ 2000, and sure enough, it outlines that air passageway. What it
DOESN'T outline though, is what seals up that passageway when the trigger is not depressed, so I have no idea how to resolve that. It's definitely something inside the handle that must regulate that passageway.
I'm attaching the diagram if you're curious, but that's definitely the issue. For once it's nice having another gun that's mostly identical to compare to. I know it's not ideal, but unless I can figure out some clear cut reason why that passageway leaks, in the end, I'll probably just sell the gun for parts as investing $100+ on a unproven spray gun with proven issues doesn't sound like a smart move and it doesn't appear like anything in the rebuild kit itself has anything to do with the internals in the actual handle.