There ain't no misunderstanding. One speaks in a way not to be understood, no one understands, so why waste typing time?
Pond separation does cause problems. KDXs not in the US are often NOT US bikes. They are SRs. SRs are considerably different from US models, so any 'advice' from a US KDX owner to an SR owner may well be worse than a waste of time, 'cuz it will be WRONG..not simply not applicable.
That seems to happen more often in NZ and AU than in the northern hemisphere, though.
Anyway...to your post..........
If you have oil spitting out the pipe/cylinder joint, it likely is NOT a 'collar' (gasket) missing, and, no, they don't all do that.
Chances are your pipe is bent. That's common. If you dry fit your pipe, you will likely see that the pipe head-end is not square to the cylinder. If it IS fit square (even depth all the way around) when you put it on, likely the silencer/stinger end don't line up..the resulting tweak to get that joint together UNseats the pipe/cylinder joint.
A couple of things: Bend your pipe to make it fit on both ends like it should. Aftermarket pipes are pretty easy to bend. Stick a piece of pipe in/on each end, move ends as required. With a good bit of patience and some pondering over the geometry of the situation, you will get to the point that the headpipe/cylinder joint is square and it does not MOVE when your put the silencer on.
There is also a good chance your patience with fussing with it will dissipate long before the fit is finished. In that case, put a bead of hi-temp silicone around the outside of a clean headpipe end, place in a clean cylinder. Attach the springs/hangers, put on the silencer, let the joint set until the silicone cures. A trouble light (incandescent..not LED or fluoro) hung near the joint will help the cure process.
Re: Who's right? (oil)
Its largely a matter of personal preference. I've found 40:1 works better in my KDX than does 32:1. That is anti-thetical...as the more oil is used, the better a 2-smoke has been documented to run. Still...40: is my choice. I prefer 32: in my Banshee twin over 40:. My choice.
Any KDX skidplate I've seen has protection for the existing frame loops that already guard the 'sump'. Some bike skidplates do NOT have those 'ears' as an integral part OF the plate.
'Frame guards' generally refers to protection for the frame at boot-wear points. Devol and Works Connection do make guards that protect that part of the frame. 'Frame guards' is not generally a term referring to the FRAME LOOPS that protect the mag/flywheel and the water pump. The loops don't guard the frame..they guard the motor..the loops are PART of the frame.
What tire pressures you generally run? The lower the better, pretty much (within reason of course. I'm not talking about 2psi..or whatever the hell newton-meters/kg squared excuse you use for pressure)..as long as your tube can protect you from pinch flats (a heavy duty tube) and you don't hit rocks hard enough to damage your rims at said pressure.
Jeb: Who's Bob?