Is the GS brand the same as GSO brand?
If it is anything like this scope:
http://www.productreview.com.au/p/pr...203eq1v-a.html
I will suggest that it will have a spherical mirror.
There is another way to test this. In a lot of the bottom-end Chinese scopes, they have a corrector lens in the focusing train, between the eyepiece mount and the secondary mirror.
If you like Neil, you can PM me and I can swing by and take a look. I live close by to where you are.
EDIT: What you are describing sounds very much like the 6" Chinese one that I first bought. Everything looked like it had a comet tail on it, and no amount of fine adjustment would remove it. I ended up pulling it apart and giving it a good clean up, but the aberration was still there, due to a spherical mirror.
Just click on my name at the top of this reply, and choose the Private Message option.