I have also removed these and found no pinhole. Then I could not get the diaphragm back in as they fit with a bit of precision.

So I used some synthetic wheel bearing grease to lube up the rim of the thing and it slipped back in. This also sealed up my leak as there was no pinhole. It was leaking around the rim.

I then removed it again and treated it with glycerin to renew the seal. And it held.

I do not know if this is a fix or if I just got lucky.

I have also used this trick to renew vacuum trunk actuators for 60s and 70s GM cars.