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First question: I'm not sure you can actually change the size of a brush when smudging. The option might be there, but I haven't seen it yet.

 

 

 

I believe the healing tool should be there in the toolbox (or whatever it's called). It's there for me, the symbol is two crossed plasters.

 

 

 

I don't know if that's helpful, but I use Gimp on a Mac too so I know a (tiny) little bit about it. You might have a different version though.