A bunch of carb/air filter questions

This may be a series of stupid question from a newbie.

Air filters can be cleaned, right?

I started cleaning my carbs last night and discovered a couple of the o-rings were dried out and brittle. They need replacement. I was able to carefully separate the gaskets from the bowls and the carb covers. They are in good shape.
I am trying to avoid the cost of $100 for all new gaskets/o-rings as part of a carb overhaul set I don't really need.
1. Can I reuse the gaskets if I seal them with some RTV or similar?
2. Can I buy just any rubber ring of the same size?

I am guessing not on question 1. But I think I can save a chunk by making my own gaskets. Are their any suggestions for materials. They look like paper gaskets?

Lastly, is it normal for two of the choke plates to have a little trap door type thing in them, and two to not have this trap door?

Any help or advice on any of the above would be great.
Thanks!

you can trace the gaskets carefully on a cereal box. a little trimming and being carefull they work good.check your local parts store for the o-rings, you'll just have to match them up.