Replacing fuel cells on just about medium or large helicopter and then seeing no drips you go home happy, only to find a puddle in the morning. Then you get a deserved reaming from your domestic partner for putting jet.fuel smelly clothes in the machine at home, thereby making it a bad day all around. Better yet, on an AW 109E, I once had to put 3 different NEW fuel cells in before I got one that didn't leak right through the fabric but not until they had been in service for a day or two. These were not pin holes but whole sections of bonded bladder that just leaked. And another one, is putting a self sealing tank into an OH-58, especially if the bladder is a little old. Like putting 10 pounds of you know what into a 5 pound bag.