Why not just spend the $5 on another master link and get it done right right now instead of having to worry about when/if it's going to fail and dealing with it down the road?
The shop that looked at it didn't think it was worth it. This is the shop that I went to in order for them to change it out. He inspected it and said don't worry about it.
The way I see it is the same as having a ding in the tank. I have a ding in both sides of the tank and I don't worry about it. It's been that way for years and there is rust there, but I don't worry about it because it really doesn't make a difference.
IDK what the failure point is on those o rings, I've heard some people get 25 40K+ miles from a chain. The shop said it's not going to make a difference. Just like looking at the tank and saying why not get the dents fixed... they are rusting the tank. I don't see it that way, the damage to the o ring or the tank isn't worth worrying about.
Worst case, I'm 100% wrong and that o ring is gone next month, in that case, I replace it for the same cost as replacing it today. Best case, the shop is mostly right and it last 25K miles and then fails. $200 for a new setup after 25K miles is not a huge cost. Maybe I would have got 30K, it I still say that's not a huge cost.
Edit: I might change my mind on this and next time I do this, I'll cut the extra links so that I have a guide to how thick one side is supposed to be. I have a 5" section left over, cut out one of the middle parts and use that side piece as a guide to press in the new master link, that way they'd be the same width.