The bolt shroud/firing pin assembly on the M70 comes out without tools. I don't have one, but I've taken one apart and it's about as easy as anything.
There's a little plunger on the left side of the cocking piece, push it in and unscrew the cocking piece/firing pin from bolt body. Hose out the interior of the bolt and the firing pin/cocking piece with brake cleaner or spray degreaser somewhere with good ventilation - like outside. As the manuals say reassemble in reverse order. A little light oil on the firing pin/cocking piece to prevent rust isn't out of place. Breakfree or something similar works well and won't solidify at low temps and is easy to apply.