Quote Originally Posted by sudsmobile View Post
You need to address the issue, which is that it's milk and it's in the cushion. You need to rehydrate the stain/spill with a combination of water and an enzyme based cleaner to eat the proteins that will eventually cause it to smell. Once you get the spill rehydrated, to removing as much as possible with a wet vac. Do this several times until it looks like it's pulling clean water. You can then address the staining if this hasn't done it. This is how I would do it. YMMV.
Yeah the fact that its milk and in the cushion makes this a potentially more annoying problem than just a stain. Everything this guy said is what I would have done.

Regarding the stain though, you could also try something like the leatherique system. I know it's not made for treating stains, but I've seen it help with getting ballpoint pen stains out. I doubt it'll do much with this though.