The 10K reference is just a contingent liability predicated upon the success of the current proceedings against TTCM. It isn't an admission of liability and it doesn't make TTCM liable for the default judgment.
Unless the original judgment against the former sub was obtained by fraud (lying to) the court, I don't see any way to have that judgment set aside at this point, but TTCM doesn't need to have the judgment set aside in order to prevail in this case.
The default against the former sub is useless (an "empty judgment"), unless the complainant is able to enforce against TTCM. TTCM was not a party to the original proceeding against the former sub, and therefore is entitled to raise every defence that the sub could have raised in the original proceeding. In effect, TTCM is entitled to a trial on the merits of the original claim if it is to be found responsible for the obligations of the former sub. TTCM is also entitled to various other defences specific to the cause of action that allows the complainant to try to enforce the default judgment against TTCM in the first place.