There are actually two separate problems with the bent models.
(1) Model comes out of the mold okay, but gets bent in transit. The Hot-Water Trick works perfectly for this, as long as you heat the model thoroughly. The fix will be more or less permanent. In these cases, often, there's not even a need to re-shape the offending bent area manually ... because the plastic has "memory," simply exposing it to hot water allows it to take its molded form.
(2) Model comes out of the mold bent (or in a substandard pose). One example of this is the vrock; I suspect the gnoll skeleton is another. In my experience, the Hot-Water Trick, no matter how thoroughly performed, won't be a permanent fix for these models. Again, because the plastic has "memory," eventually (and very gradually) it slips back into the form in which it came from the mold.