RE:WD 40 and Fly Lines
I use WD-40 routinely on plugs, particularly if there's a chance they've got suncsreen on them. Can't say for sure, but I believe it helps. I also believe that DEET or sunscreen on lures is detrimental and that WD-40 counters that. haven't tried it on flies, but did find that a little silicon lubricant sprayed on the line or on a rag through which a line is pulled, is a nice quick way to put some slick on a fly line.