Check the inside of the oil filler cap, if it has a white residue deposit, then you have moisture in the oil. Very unusual for BHG on a Supra, they normally go between the combustion chambers and coolant.
White residue in the filler cap sometimes accrues if the engine hasn’t been run for a long time. (Like stored over the winter period) or had a recent engine overhaul. Not normally an issue, but it could be in your case.
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