Yes, leathers for the majority are almost entirely dependant on light, so much that its really not required or even recommended to feed phytoplankton. So, usually when you acclimate the new leather to your tank it will produce a mucous coating to protect itself from the shocking changes in temp and salinity mostly. They may also look "wilty" or dried up mostly due to the same reasons. There shouldn't be any reason to be alarmed though because this is common and leathers can handle this pretty easily. For the most part they are a very hardy coral with the figi yellow leather, sarcophytum elegans, as the exception being much more sensitive to changes becoming infected easily. Anyways just give the leather ample non-laminar, random flow to break up the mucous and slowly give it more light over a few weeks time period so not to shock it. They are very hardy and should be polyping in about 2 weeks if all goes well.