The shadow is missing on the actual legs - Perhaps, considering that you're using a *.png, you could make a semi transparent "blackened" out version of the top of the turret, and draw that above the legs, but below the turret's top but shifted slightly to the right and down. That way the turret looks like it's casting a shadow onto it's legs and the ground below.
It's a quick and dirty method, but it would work.
Let me work on the script and I'll upload the finished version of what I meant =3
(Of course, I'll give you the link to the Host-A file, I won't ACTUALLY upload it here, but on a filehost for you to download and check out)
*edit* Well it doesn't look like I'd be able to edit any scripts, sigh, so you'll have to add the shadows to the physical legs.