[Is there any particular model or production year to stay away from?] - Nope
[Any inherent problems to look out for?] - Yes:
1) Shoot only what the gas system was designed around - 240gr JSP/JHP ammo - NO LEAD BOOLITS.
Lead will shortly clog the gas system, leading to jamming and frequent teardown cleaning.
2) Since parts/service are hard to find, and some parts - like the trigger housing on the old (tube magazine) model - are unobtainium, any prospective purchase should get a hands-on instection prior to laying out any $$$.
Small parts are findable/repairable - but the trigger housing is not, and can crack/break it's front attachment lip where it hooks into the bottom of the receiver.
A bad one can be tested for, while in the stock, by trying to flex the front of the bottom metal up/own in relation to the receiver.
ANY movement would be a deal breaker for me.
Perfect-looking specimens can have a broken housing, while beat-looking ones work perfectly - look them over.
A "tell", of one that's been little used, is little-to-no-wear on the magazine latch - which gets depressed by cartridge noses to load the magazine.
The anodizing wears off the central part of the latch button/fingerpiece with a lot of use.
BTW - None of the issues under #2 above would apply to the new model .44 carbine - the 99/44 Deerfield, which is basically a Mini-14 on steroids - detachable rotary magazine, et al.
Some like them better than the old model, some don't. YMMV.
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