MC,
I'm not sure what is being "inferred" with the mention of New or Old models re: the 917M II........But I will tell you this.........
Marlin 917 Mach II's were notorious for cracking stocks. We were quite busy at one point, making and installing replacement stocks on the 917M II Auto loaders. We also were re-reaming the chambers in an attempt to solve the problems with that rifle and ammo..
I bought a group of (4) 917M II's (Autos)for myself, and relatives.......3 of the 4 have blown the stocks into three or more pieces.....Luckily, no one was hurt. I began shooting my rifle with gloves and safety glasses after I saw the first one explode..................Mine blew up 7 rounds AFTER having the chamber reamed.........
The cartridge cases was said to be improperly annealed, and then the powder was said to need to be modified, etc, etc.....bottom line is, The 917 is capable of delivering some SURPRIZING performance when you and, maybe your children least expect it!
If I were you, and wanted a 17 cal rifle, I'd forget any ideas of owning a 917 Mach II Auto, and turn my attention to the 17HMR round.............
After my experiences with the Mach II, I won't even consider a 17 rimfire.................
I used to own a BSA bolt actioned rifle chambered in 17/218 BEE, that would chrono spire pt rounds at 3900 FPS........I sold it, thinking it was too specialized for my needs....That was in the early 80's....Wish I still owned that rifle!.......I still have a few rounds for that rifle.
The above, is my experience with 917Mach II's...............Yours may be somewhat different..............
Tom