Getting everything out of the barrel is the hardest. I got a rubber cork and plugged the muzzle end and then filled it with simple green and let it sit for 20 minutes. Rinsed with hot water, then repeated 2 more times.
No, the cosmoline darkened the stock. It lightened up quite a bit as it started weeping out of the wood. I didn't do any refinishing to it. Also, be careful with the front hand guard. It's pretty thin and it can crack pretty easy.