I said something similar my last time around with primuliflora. Jimscott seems to have hit it right on the head when he said it was too much change too quickly. Mine are now thriving in a loosely covered fish bowl on a north facing windowsill. You may want to try using 100% LFS about 3" deep. Make sure you wet it thoroughly before transplanting. This helps keep moisture near the plant. Every time I noticed leaf rot beginning I clipped off the affected portion immediately. The rot seems to spread when left unchecked but trimming prevented it from progressing on the leaf. Don't give up the ship just yet.....there's plenty of primuliflora "exorcists" to get you through.