Can't do much about missing clues, but I'm surprised by xword "solvers" having to ask for help with clues.
Without wishing to sound smug, (which usually means the opposite)the RT cryptic xword can be solved every time, usually wuthin a short space of time, so no need to ask the nerdies for help!
In our days of the PC, (computer, that is, not the copper or the Brussels beast) unless you are a Troglodyte or some such similar cave-dwelling hermit, you should have, or have access to, a laptop at least, and here you have the world, so to speak, at your finger tips, it's just a matter of using your loaf about searching. I have used this method and it's pretty well foolproof every time. Some may feel it's cheating, but it's only a little further along from asking for added clues (!)
And now for something completely different.
I was in my local hardware store today, and was amused by the instructions on a roll of repair tape for split or leaking pipes, it read, 'make sure all surfaces are clean and DRY!
Good luck with 21 down, but if you're really stuck......