I did read somewhere that the current owner has to accept liabilities of previous ownership and thrash it out themselves.
This is true – that’s why these agreements are enshrined in by-laws, so that they survive transfer of ownership. However, there are avenues available to the new purchaser to pursue the vendor for non-disclosure that a liability existed that they knew about or should have known about.
You could even turn this back on the OC and threaten to take it to NCAT for failure to fulfil its responsibilities – i.e. pursue debts incurred by the previous owners. That’s a long shot but it might get them to back down if there is no evidence that they previously sought the payments from the owner.
Either way, you should at least chat to an experienced strata lawyer to discover what your options are and find out if the cost of putting things right would be more than just paying the bill.