subject cleaning

I'd like to do some subject cleaning with procmail so that:

 Subject:  [Fwd: Re: misc stuff]                => Re: misc stuff (fwd)
 Subject:  Re: [Fwd: Re: misc stuff] (fwd)      => Re: misc stuff (fwd)
 Subject:  [Fwd: [Fwd: Re: [ace-users] misc stuff] ]    => Re: [ace-users] misc 
stuff (fwd)

I have the following recipe that only handles the first case:

:0
*$ ^Subject:[ ]+\[Fwd: \/.*
{
    sub = $MATCH

    :0
    * sub ?? \]
    * sub ?? ^^\/[^]]+
    {
        sub = $MATCH
    }

    :0 fhw
    | $FORMAIL -I "Subject: $sub (fwd)"
}

I need help to get it work with case 2 and 3? Note the [Fwd: .* ] can
be multi-level nested. It doesn't look easy for me.

Thanks in advance.

Tony