Please don't soak pearls in anything. Every original set of pearls I own have rust on the inside. If it bothers you, take a small rag with CLR and wipe the rust spot until it disappears. When done, wipe with wet clean rag.
I would say they are too thin to be original. By my observation, factory pearls are as thick as hard rubber stocks. I measure about .35" at the thickest spot on one set of I frame pearls I own and a second set I believe to be post-factory .28". It is an inexact science, but thickness that matches hard rubber stocks in any frame size indicate they would likely be original. Perfect fit also lends to authenticity. Lastly, imperfections, imperfect rounding or shape, and or hollows in backside would indicate distributor post-factory pearls. Check yours with a micrometer if you have one at the thickest spot and inspect them carefully. Also, let us know the serial number and we might be able to tell you appropriate ship date.