De-lid successful, replace TIM with gelid extreme as it's safe (non conductive) and superglue the heatspreader back on using tool that really inspires confemidence. Eat while glue dries, put back in the mobo with the crappy stock cooler it was fine with yesterday and - it doesn't boot.
Popped it off again to have a look, found I used way too much paste so cleaned it up and now waiting for glue again 
DO NOT use gelid, or the glue..
The Gelid is worse than using AS5, because it's so thin.
THe thinner the paste the faster the Pump-Out, whereby it gets squeezed out between the IHS and the die, because those surfaces are so smooth, there's nothing to grip onto.
You need Liquid Ultra for between the Die and IHS..
DO NOT GLUE the ihs back on.
Just set the lid 1 mm above where it originally lined up.. THen as you clamp down, the friction should slide it about back to the right place..
(the placement doesn't really matter though, as long as the side clips are firmly there.. and your mounting doesn't wobble.