Wellll.....the ONE thing he MIGHT have killed internally is the plastic buffer.
As he pointed out, it's a 1970's Squirrel-Stock 18-round mag Marlin 60.
Which means, usually, it's high time to replace the buffer & the recoil spring.
The original buffer is white plastic, the new ones are Black.
You can call Marlin and order direct from them...or Numrich, or Brownell's...etc...
I betcha if you were born in the 70's your buffer ain't so springy anymore either