I guess it depends on how bad the leak is. If it stops it and it stays stopped, yeah, I'd call that permanent. The Lucas and Blue Devil stuff both only soften seals but do not dissolve and swell them over time like some of the older stuff. And no, it will not hurt your engine. I am running some of the Blue Devil general oil stop leak in Kitty's car now. It has a main bearing girdle that bolts to the bottom of the block that holds the crank in. It's sammiched between the block and the oil pan. They used a rubber o-ring style gasket for the oil pan side and that Ford grey sealer on the block side. It's a common problem on the 3.0 for the sealer to fail......and ours has. The engine has to be removed to repair it. I'm not ready for all that right now. The only one drawback is you must add the stop leak back when you do an oil change.
