My plan, if I have to replace mine, is to buy a cheap one then when I replace the OEM one I will strip it right down and clean it. If I knacker it, well, it was for the bin anyway!
I'm not sure if you can get them them apart, not without some significant mangling. The one on mine is all crimped together, couldn't see any easy way in. However, if it's just sooted up, you can clean it reasonably effectively with a good dose of carb cleaner.
Once you've removed it, turn it upside down, fill it with carb cleaner and leave it for a while to soak. Then give the valve pintle some work to clean the soot out of the bore. You have to insert a thin blade between the pintle and the seat before you can get a hold of it with a suitable implement, before giving it a good bit of in-out working against the spring, together with a few good squirts of carb cleaner. Take care not to mark the valve internals, but the pintle is made from very hard steel, so you would have to be pretty rough to damage it. The valve casting is easier to mark, so watch that.
It's surprising how much muck comes out, and ours has been okay ever since.