If the circumstances have changed, the appropriate course of action would be a further cease & desist. This would allow Padmapper the opportunity to desist from their activity which is always the right course of action before instituting proceedings.
The C&D mentions not just accessing CL content, but republishing it. That the content was transmitted through third parties is irrelevant for this copyright claim.
It may be irrelevant, however you will get penalised on costs (at least in the UK) if you do not attempt to resolve the dispute prior to issuance of proceedings.
I personally wouldn't want to risk the ire of a judge in issuing proceedings when at least on the face of it, PM complied with at least part of the initial cease & desist sent by CL.
As others have pointed out, it's not Craigslist's content. According to CL's own terms, users own all content posted on the site. So CL has no copyright claim on it.
