Likely, he won't need any more surgery. Dogs are very vascular around the testicles, so often after castration, leaky vessels empty into the scrotal sac and cause the swelling. It does take a long time to resolve, but it usually doesn't require more surgery. With Cole, the vets waited for the leaky vessels to close themselves off and then aspirated some of the fluid out of the sac to help give the healing a bit of a nudge in the right direction. It took a few weeks, but the swelling finally subsided on its own after the aspiration.
It's a good idea to keep him very quiet for another week or so to allow the vessels to close off.
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