Airlines that I've been associated with train to use "Panpan" or "Mayday", but if you are dealing with ATC while working a problem and haven't yet decided to declare any kind of emergency then stating it in clear language shouldn't be a problem in North America. However if you want their attention out of the blue then prefacing your transmission with those words will have ATC paying very close attention to what you say next and shut everybody else up at the same time. Also anywhere else on the planet with the exception of the UK declaring as per the AIM is a very good idea because it may be the only words ATC understand.
"Not only a slat problem but for some reason when the slats jammed the thrust went into thrust lock at only 63%, hence the comment about being unsure whether they could maintain their altitude."
With a flap/slat problem the AP and A/THR automatically disengage. Since it is an uncommanded A/THR disengagement the FADEC is programmed to lock the thrust in the last position. The crew still had full control of the thrust in manual mode, however it required them to actually move the thrust lever. Once the FADEC detects thrust lever movement following thrust lock the thrust is set to the lever position. When the crew got around to completing the ECAM procedure for thrust lock they discovered this.