Time to replace chainring? I ran a squeaky chain for a while on my bike and subsequently destroyed the chain and the cassette. Both were swapped out at the exact same time for a new chain and cassette. 

Now I am afraid that the chainrings have been damaged. I suspect that the chainrings have been damaged because it's only been about two months with my new chain and I am not a frequent rider. I ride in almost pristine conditions - I ride on regularly maintained roads and have NEVER gotten a puncture on the road I put in most of my miles on. I only put about 500 miles (if that) on this chain. The path is dry and the only objection that one might be able to raise is that it's slightly dusty at some points. The only maintenance I've done is a few squirts of White Lightning Semi-Dry Lube after breaking in the chain. It came to me pretty greased up so I left it as is until I rode it for a fair bit before giving it a quick shot of lube. 

So I'm pretty surprised that my chain looks to be pretty worn judging from a quick ruler measurement. 

In the attached pictures I have lined up the 0 marking on my ruler with the end of a roller and from what I've read online, if a chain is new, the 12" marking of the ruler should be covering up most if not all of a roller. On my chain the 12" marking is barely covering up a roller. I've taken the chain off the bike, yes, but I've stretched it when laying it across the ground. Even on my bike where the chain has been tensioned, the 12" end of the ruler still fails to cover up the roller. 

I also did an informal test in which I shifted the bike into the big chainring and pulled on the chain to see how many teeth I could expose. I saw at least 3-4 partially exposed teeth with this method. I read that if you can see more than half an exposed tooth, then your chain is stretched. 

So:


Should I consider replacing the entire crank or just replace the middle chainring - the one I use 99% of the time? I have a Campagnolo triple crankset, 9 speed. It's also square taper. 
Or should I just start leaving the chain on the big chainring which has seen probably no more than 5 miles (seriously)? 
Is my chain really stretched? I read that some chains show a high initial stretch reading when new, but this isn't really an indication that they're done for. I have a KMC chain if that matters.
From Sheldon Brown


  The normal technique is to measure a one-foot length, placing an inch mark of the ruler at the side of one link pin, then looking at the corresponding link pin 12 complete links away. On a new, unworn chain, this link pin will also line up exactly with an inch mark.


From what I can see in the second photo, the edge of the ruler represents the 12 inch mark, which lines up exactly with the middle of the pin on the end of (what I assume is) the 12th link.  The chain looks fine to my eyes.  (For what it is worth it has been my experience that KMC chains are pretty tough.)

The difficulty with using a ruler is also why chain wear tools also exist, these also include wear on the rollers as part of the measurements (which measuring the inter-pin distance will not consider).  Worn rollers will affect the realized pitch of the chain.

If your chain ring is too worn, the teeth will look like a shark fin and a new chain will slip under pressure.  For more info see: Does this chainring need to be replaced?  If your middle ring does go, I would suggest looking at replacing it before you change the whole crank set (Just my opinion!)