After baking the pavlova, let it cool and cut it in half. A moist liquid-like substance appears inside. (It does not leak out) Is this not ripe?
I baked it for 90 minutes at 120 degrees and cooled it in the oven for about 2 hours before cutting it.
It sounds like your meringue is "weeping". This happens when the egg white proteins contract too much during cooking, squeezing liquid out.
Overcooking meringue leads to weeping. Using a small amount of starch in the meringue can help. So can pre-cooking the meringue by using hot sugar syrup (so-called "Italian meringue", which I think is unusual for a pavlova but I could be wrong).
Ultimately, though, it's really hard to reliably prevent weeping, and it does not indicate that the meringue is undercooked, unsafe, or un-delicious. Unless you can't stand to look at it, don't worry about it.