My father in-law heard that I had an AR and sent me the 7 mags he brought back from Vietnam along with a cleaning kit and his helmet band.  The mags look their age, but seem to be in good order. I am torn wether or not to rebuild them in order to be sure that they will function reliably, or just keep them as they are and spend the money on P-mags if I want reliability.  It looks like a rebuild kit is about half the cost of a new 20 round mag and cost is a factor for me, along with the sentimental value.  Thoughts?

When I was 16 I bought a Stratocaster with money I'd saved from working a few dollars at at time. I still have the guitar, play it regularly, would use it for a gig without hesitation.  But when I joined a punk band in '90, I wasn't about to let some stage diver take it down.  Bought a cheapie clone and threw a pickup in it for punk gigs.  When the punk gig was over, gave the guitar to a girl.

Save the Nam mags, they're relics from a bygone era.  Buy some new production to use as range dogs.

+1 on leaving them as is.  Refurbishing them would probably work, but why risk it, they're a part of history.

~Augee

ETA:  I'm just now concluding that you probably were gifted 20rd mags... Is this the case?

I'd leave the vintage VN mags as is.

If expense is a main concern here's what you can do...

Function test the Nam era mags.  (If these are 30 rd mags, you could put new green A.T. followers or Magpuls but keep the original followers stowed and clearly marked for future reference)  If these mags are the 20rd version, I'd clean them & ensure the springs are installed correctly.   If the mags function- if they are 20s w/ the alloy followers they probably will unless damaged- you have 7 mags that work.  But, if you don't want to wear them out... You stated above that rebuild kits cost 1/2 the price of new mags.

Buy 3 or 4 new mags (Half the cost of 7 rebuild kits) and now you have 7 vintage mags that you've ensured are reliable and 3 or 4 new ones to take out/test and use daily while keeping the vintage mags in reserve.

Sentimentality can be hard to explain to others but I do get* your sentiment.  

Sly

It sounds like you want to shoot with them, and haven't yet. Shoot them.  10 bucks says they will work.  Why change anything?
I'd keep them as is and shoot them if they work, and if not, put them on the shelf as a momento and get some fresh mags.

  Those 20rd mags given to you are some of the most reliable mags for the AR platform. Used or not. Unless the alloy follower is chewed all to hell, the only think you might need to replace is the spring.

  Congratulations on your mags and a FIL that has apparently taken a liking to you.

Thanks for the advice.  The concensus seems to be that I should keep them as is, which I think I will do.  I was surprised to hear that they would still be in good order.  They do have the alloy followers and with only one exception, seem to be clean and ready to go.  I do hope to use them and turn them into a bit of a conversation piece.

IMHE
ALL of my early Nam era 20's have been 100% reliable to date
if it were up to me i would leave them original and use them once in a while on special occasions lest they become Objects D'art.  Think of the heirloom factor when you someday say "son, your grand father used these magazines in vietnam"

The straight body 20 round mags are very dependable, there rarely is a reason to rebuild them unless something actually breaks, brush them down inside and out, load em up and shoot shoot shoot, thats what they were designed for.

I have a dozen 20 round mags I brought back from VN, 6 M-14 mqgs I brought back from Berlin and 10 15 round carbine mags I borrowed from a NG unit I was with in 1963 after I returned from Berlin.  All of the work.
I used 3 of the M-16 mags in service rifle competition for 20+ years, they made nine trips to the All Army matches in Ft. Benning.  Still going perfect.  I bought 4 stainless CProducts 20 rounders to replace them but they are loaded and sitting in a tactical bag.  I just don't want to replace my old reliables for competition, some bad ju ju there.