I've had my new SGS rear struts for a good few months now but they are still very sticky and I have to push the tailgate up to get it to go all the way, is this common or should I contact them?
It is common. The failing to lift is because they have not put enough gas pressure in them. I sent mine back and they re-gassed them to a higher pressure but it was shortly after I'd received them. You can try your luck.
Mine also creak so I won't recommend them to anyone else. I'll be going down the Magneti Marelli route next time.
I fitted Magnetti Marreli from eastern europe about £20 delivered and they are absolutely spot on, no more tailgate dropping on my head whist I go to get something from the boot, think they are specified for a BMW or something lol. See boot strut thread for details...