I'll admit to knowing nothing about rats, and i do think Jason looks a stunner

Have you asked the Vet how long to wait after the op before putting him near your girls?

With my ferrets, all males castrated, occasionally vasectomised I was told to wait 6 weeks, so I do.
I did have one that wasn't vasectomised properly and i had serious doubts wether he had been done at all, so putting him to the in season girls, to bring them out of season, produced 4 litters So now I am extra extra careful!