Jose, the reason why posts like this are problematic is the average person reading it doesn't know that your roof underneath is completely rotted, nor would they be expected to know this information. Somebody searching for sewer vent repair tips might see what you have done and think that they can make the same sort of repair and have it last for the next 10 years as you seem to imply. 6 months later, they are back on here complaining about water leaks and soft spots.
It is well documented that Eternabond does not stick well to black ABS pipe. After a couple of good rainshowers, you will be back to square one with water leaking in.
If your roof really is as rotted as you claim (and I have no doubt based upon the photos), you should give consideration to gluing down the bottom vent collar with liquid nails, then Eternabond over the perimeter. You will end up with something like this:
Finally, snap the vent cap on. This approach
will keep the water out. What you've got going on with taping the pipe up and putting a cap on is just hokey. Sorry if you consider that rude, but I don't know any other way to describe it.