The seller of the ebay frame responded with this, fwiw:
Hi. thanks for your interest.
well, as far as I know this model came out in the second half of the 80ies. it wasn´t produced that long and therefore it is rare and hardly to find now. in the cinelli hierarchy all the SLX models were top of the line in their classic steel era. in the 90ies they came out with new steel tube sets like Columbus Nivacrome and Genius before they opened their production for Alloy and Carbon materials.
hope I could help you.
cheers,Achim