Maybe a machine shop can disassemble it for you and find the source of the seize of not merely the piston rings corroding into the cylinder wall?

Else, maybe a bind from a something out of spec? A bent rod or crank?

Coolant loss and remaining engine heat can cause havoc for engine internals.

Stock Turbo B21 or did you have the boost dialed up much?

Some will suggest using Marvel Mystery Oil in repeat applications to see if it frees the motor if seized at the piston rings-cylinder wall? Maybe a gentle tap-tap using a wood section with a light hammer.

Do the connecting rods move along the float from to rear? Does the crank shaft exhibit any movement along the end float front to rear, if minor.

The engine coolant is corrosive and carbon steel will corrode after exposure and left to set. The antifreeze part of the engine coolant is also hygroscopic. The water part of the coolant evaporates, yet the coolant coating the internal engine parts may have a wetness to them that helps the remaining coolant coating engine parts to corrode.

Else, I'm unsure. Hopefully other can help.

If not already, please search and ask at the Turbobricks form. Better ease of use with an account at the Turbobricks:

http://forums.turbobricks.com/

Hope that halps yoo.

'Tis the Egg Nawg Holidayze here and now. Eggnog ice cream at the Walmart.

Whoop. Eeeee.
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Beh.