Why not use proper roof sealer?
We use
RJ LONDON ROOF SEALER and it worked 1000% better than Vulca-seal or any other elastomeric roof sealer.
For small holes or gaps, just paint it over with RJ LONDON ROOF SEALER.
For larger gaps, use a piece of cloth to help bridge the gap and paint it over to make it water proof.
BTW, it comes in colors so you can color match it with existing roof color.
We even used it for our delivery truck's cargo area when it leaked. It lasted around five or six years. We just re-applied the sealer and the leak was gone.
Available at WILCON and at other similar stores.