Yes I would use it just until you get time to do a matrix swap, although I've known it last years, I just don't like the thought of relying on it.
I used it as it was winter time and didn't fancy a hg swap at the time, just to buy me some time, but can say for sure it did not block any water ways, there was no trace of it when I took the head off, even though it had worked sealing the blown hg.
tabetha