When this,the last of the line of Leica enlargers appeared on the market in the 1970's it had either a 40mm Focotar lens or a 50mm Rodenstock Ysaron 50/3.5 lens. I have been unable to find a good reason for the alternative lens but it may have been a question of supply problems with the Focotar.
Actually, any other 39mm thread lens will fit but for autofocus you have to have one of the two named lenses with its factory fitted cam. Over the years I have picked up several 40mm lenses which may be used with only small manual adjustments to focus. Of all these the Apo-Componon may lead by a very short head at present and they are illustrated below. These enlargers have fallen way down in price and may turn up without the makers lens so all is not lost so long as one does not mind checking the focus manually-but you are going to double check with a magnifier anyway-belt and braces.For me,the most tactile is the Nikon lens and the least pleasant to handle is the Leica which has a strange feeling plastic outer coat.However, the Leica lens is probably equal top in performance judged simply from the prints it has produced . Well worth remembering is that all these short lenses are intended for diffusion lighting and not condensers.