Do you take your guinea pig to a vet when it's ill?

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I just noticed my guinea pig has a strange growth under his right eye. His eyes are black and the growth or cyst or whatever it is is white, so it stands out. It's at the bottom of his eye, curved and narrow, like a new moon shape. He doesn't seem to be in any pain and he still eats well. I am torn about taking him to the vet, however. He is my pet but the cost of having him seen makes me wonder if it is worth it. He is adorable and sweet and doesn't seem to be suffering. Do you take your guinea pigs to the vet when they have eye problems or seem unhealthy?