Coat the thermostat studs with Permatex (Loctite) non-hardening gasket cement. They will always pull apart.

Anti-sieze is a good option if you have it lying around, so would stainless steel studs if you plan to own it in the long term...

I've never let my cooling system go so long as for massive corrosion to occur, nor do I reuse crummy bolts or studs. It's a problem I've most found on engines that have been neglected for some time.

Using a soft touch when it comes to screwing them in and out, and checking their condition will usually stop the problems.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Not wanting to tell you how to suck eggs or anything with these suggestions...but

* make sure your cylinder head is worth putting back on before you spend too much time on it. Look for cracks and warping, as well as corrosion on the thermostat sealing face. Mine was corroded in this area and caused never ending coolant leaks up past the thermostat cover studs. A bit of mastergasket fixed the problem but the next time the head needs to come off I'll either need a bit of welding done or I'll need to find a replacement head.

Look everything over first and save heartaches and frustration later. Take heaps of pictures, download them to your computer and look over them before you reassemble everything. Saves me everytime!

All the above info is spot on the only additional thing I Ciyld add is rember after running for around 200 K's to retorque the head and re adjust the taps again

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Stop Licking the Dog...I Don't Care Who Started It