Have you ever fired it before? You never indicated in the OP, rather it was only implied.
Pull the firing pin spring and put the firing pin back into the stripped bolt. Use something to push against the rear of the firing pin and measure the firing pin protrusion. I cannot remember the spec for Marlin but it should be around 1/16" (.063") If you don't have the means to measure it then just look and try to guess. If it doesn't come out far enough then there might be a burr on it. Check when you disassemble the bolt again.
Try different ammo. There might be a bad batch that has the rim thickness out of spec.
Headspace might be so loose, the cartridge is pushing forward upon being struck with the firing pin. One field expedient method is to chamber a factory round (better to use a dummy round or a full length resized case). Then with the bolt fully forward and the hammer cocked or much safer to be half cocked, try to move the bolt back and forth with your fingers. I had this problem on my 1894 44 mag. Gun still fired though. Another way is to use pieces of tape of known thickness and place them on the back of the cartridge case and try to close the bolt fully. If it closes add another piece of tape until it doesn't close. The measurement of the number of pieces of tape before the bolt would no longer close and the measurement after the bolt would no longer close will give you a headspace range. If it is more than maybe .008" it needs the headspace fixed. My 1894 was something like .016".
The locking block needs to be in the fully upward position upon the round going into full battery. If it is not then the rear firing pin plunger may be hanging up slightly.
Some folks say the extractor can be the problem if it is worn and not holding the cartridge tight against the bolt face.....this would sound like bad head space to me but it may be worth a try. Marlin extractors are consumables in my book.
