The Apeks spares kits AP 0241 (1st stage) and AP 0219 (2nd stage) are both compatible with O2 use, except for the porous filter (AP 1406) mentioned earlier HOWEVER......
They are not "oxygen clean" when supplied from the factory, they and the reg should be cleaned to O2 standards on build-up, and recleaned yearly or sooner if a bad fill or unknown air has been used. The manufacturers cover themslves by saying anything more than 21% O2 is EAN.....and most of them now "recommend only Oxygen comptible lubricants"
The main point that some people miss with EAN is that the weakest bit in the system is the O ring in the cylinder pillar valve which takes a hit of 100% oxygen at anything upto 100 bar when filling a cylinder with an initial "lump" of oxygen before topping up with air to make the 232 bar of 40% O2 EAN. This does not apply if continuous blending is used.
I've seen pictures of cylinders that became jet powered torpedoes with the combusting O ring starting the fire triangle, (Ignition, fuel, and oxident) then the brass and the other rubbery bits were the fuel and the nitrox that was already in the cylinder provided the oxygen for the jet to continue not nice...
Dont go bang go diving...
Brian C