My gelding lived for 6 years, as I mentioned before, without infections. Maybe he's just lucky, so maybe you should consult a vet and let somebody professional see his sheath - and I see you're going to do so, so I think there's no reason to be to worried about it.
Anyway, it's a good start if he lets you touch him for a few seconds. Do so, then praise him extensively. Do it several times a day, try slowly increasing the time for a second or two, then praise, praise, praise. Stay relaxed yourself.
I have come a long way, to surrender my shadow to the shadow of my horse.