I've got a strange jap Metal Slug 3 AES cart

I bought a japanese Metal Slug 3 cart of a member here once. I was told it has no manual and a tear in the spine bit of the sticker...ie a gamers cart, which is fine. At first it worked no problem on a modded system.
Now I don't have the modded system anymore and am trying the cart on a normal system, and it doesn't work. I get the Neo intro fine. But then the title screen of slug 3 is purple and has this rainbow through the middle. And then it just resets itself. I have cleaned the contacts with alcohol, and they were pretty dirty, but still the same.
Now I compared this cart to another jap Slug 3 cart. Well my strange one doesn't have the golden warning sticker on it. Additionally the cart sticker is slightly darker than the other.
Furthermore I mentioned that the sticker has a tear in the spine area, as if the cart had been opened.
This cart was probably opened. Could it be a boot?? But why make home cart boot...well, not why, but is there any stories of this having happened before?? Also, the snap lock case and insert are fine. So whats the deal here?? Any input??
And you'll prolly ask me to look at the boards inside, so please tell me how I can open the AES cart without breaking something inside??
Any input would be much appreciated !!!! Thanks you

Is the cart socket also absolutly clean.
http://www.hardmvs.com/html/slotCleaning.htm
I realise this is a home system, the idea is the same.
Dirty slot contacts seem to effect different carts in different ways.

Also, remember that there were two manufacturing runs of Slug 3, which can account for the differences. The second run did not have the warning label.

Second, NGF did make a run of slug 3's, but I think they just did the usual insert and sticker swap. I don't think they actually made bootlegs.