It is the top section (10mm shank) that has stretched.
All 6 stud collars at the top of the block were still level.
Top of this stud had stretched 2mm higher than the rest.
Upon measuring the shanks other 5 measure 10.00mm
Stretched stud measures 9.80mm at its thinnest.
Also when I unscrewed stud out of the block, no sign what so ever of metal from block threads, nice and clean with traces of the thread lock, so looks fine the block fitment.

Burton are sending me a replacement stud.

Threads on the studs are M12