She's wet inside!

About 2 months ago I found that my girl had a leak and when it rained the back passenger floor would fill up with water so I took it to the garage and they said they found a hole the size of a baseball and that it was getting in from the air vents on my hood. So I had them fix it and shes been fine ever since...ever since today! Well it rained today and when I went to go out I noticed my back floor was wet again so here is my question, could it be that the hole wasnt fixed right? (But why would it only start leaking now when its rained alot more before and nothing) or could it be that there is another way its getting in? Could there be a a seal leak near the vent. I know that water gets in there but its supposed to drop out behind the tire so why is it coming into my car. I have a 91' Z24 if that helps.
What can I do to stop this leak as it is ruining my carpeting and it will rust out my seats! Thank you for any advice!

Heater Core

If not, start checking body panels. I managed to rust out the entire rear wheel well in my 92...both sides....and the body where the shock mounts was gone too.