Your rifle has a cock on opening bolt. Watch the back of the bolt when you lift the handle. It is not going to be harder to open because of the pin spring. You should take the bolt apart again and using a block of wood, press the pin into the wood and rotate the cocking piece 1/4 turn, raise the shroud slowly and the pin and spring will seperate from the shroud. Everything will come apart from the shroud. Soak all the parts in mineral spirits. You can still have some cosmoline in the cocking shroud. Wipe all the parts well and dry. Wipe them down and lube w/ CLP or like product and reassemble.
Here are some better instructions: K98k Mauser Page