Is it running too lean and overheated? So an over expanding piston caused the seize but then cooled and contracted while not running and by the time you started kicking it over it had freed but lost most of its compression because of internal damage so wouldn't start easily and ran badly. The losing coolant sounds like excessive heat is making it expand too much in the radiator and its running out of the overflow, though not sure about that.
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After years of moaning about immigrants now i am one...