I have an 870 w/ a wood stock that is now approaching 20 yrs. old.
I have put it through less than ideal conditions
(Dropped it in pond, Dropped it 20ft. out of tree stand, left in snow,etc. etc.) and it still works perfectly.
IMHO, I would worry about the synthetic cracking or getting brittle in colder weather. I don't know where you live...but my 870 gets used for everything I hunt, year round and I've never had a single problem.
As far as a sling goes:
Have a 'smith install a stud then buy a sling that would attach to a replacement end cap.
Kind Regards,
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