[KJ223]

Hi everyone, I just swapped my cam out in my Pontiac 350, (as some of you may know from helping me in my previous forum post) and I also ended up swapping out valve springs with the heads on and the engine in the car for peace of mind. Anyway, while changing the springs I noticed each valve had a hard brittle o ring that cracked and fell off each valve, at the time I had no idea what this did, and assumed that the valve seal was the actual seal on the head at the base of the valve. After breaking in the cam I’ve been driving the car and notice blue smoke on start up, and after idling for about a minute. I realize now that those o rings that I brushed off as nothing somehow play a role in preventing this. Please try not to think I’m too big of an idiot. My question is how does this o ring do anything to seal the oil, and what is the purpose of it and the bigger seal at the bottom, (I guess it’s called an umbrella?). Why are both of these used? Also how hard is it to replace these seals with the engine all assembled now. I know it’s basically what I just did with changing the valve springs, but now I’ll just be working with the valve covers off, rather than the intake and valley pan. One last thing, I’m seeing those umbrella seals are sold as sets of 8 instead of 16, is there a reason for this or do I just need two sets? Other than some blue smoke, the engine runs great.
Thanks