Thanks Guys, yes the problems of the moulding was sorted out, they are good at things like that, PSC. There are quite a few spares in this box, but they are quite useable, something that I don't always find with PSC stuff.
Re: Marder IIs, I was under the impression that only the sdkfz 132 served at Stalingrad (which I can't find in 15mm), but have since found out that there is also a sdkfz 131 version which served at Stalingrad and ARE available in 15mm, as you pointed out! I always get confused when it comes to the Marders, there are so many sdkfz versions!