If the stick is getting very hot, you should put a fan to it.
I have a fan on it already. I am unsure as to if the heat sink is working properly :| What about the light and Core V dropping to 0?

For the back you can try these for the back. I've got them on all of mine now (not sure if they help or not, but just a little extra help if it's needed), they fit the back of the pcb/chip nicely and a plus is they are copper and come with extra pads. Down side, depending on you hub port spacing, you loose 1 (maybe 2) slots in between sticks.
http://www.amazon.com/Enzotech-MOS-C10-Forged-Copper-Heatsinks/dp/B004CL89D8/ref=sr_1_5?ie=UTF8&qid=1453580556&sr=8-5&keywords=enzotechIf the stick is getting very hot, you should put a fan to it.
I have a fan on it already. I am unsure as to if the heat sink is working properly :| What about the light and Core V dropping to 0?
Check the screws at the heatsink! Maybe they will get loose or they get stretched by heat. Its a cooling pad under the heatsink, not paste like the originals. My bitshopper-Stick has the same problems with heat and dropping VCore but i havn't the time to sort it out yet. Maybe you get the clou ...
Yeh i checked the screws before they were loose so i hand tightned them a bit. Just at a loss of what to do really. It wont run for more than a couple of mins before it stoppes and the V core goes to 0... It is a bitshopper stick. Really dissapointed.
If it was loose maybe some air got in between the chip/pad/heat sink and it's trying to get the heat out the back (?). Does the heat sink get hot/warm?