There are two separate issues here:
1. as a general rule can the EC seek legal advice without the approval of a general meeting – yes, provided it comes within the ambit of the regulations, e.g. the costs are under a certain amount.
2. can an EC seek legal advice/take legal action to overturn a caretaker agreement under section 183A which has been approved by the OC at a GM? No it can't, because the agreement has been approved by the OC. If an EC tried to take legal action it would be seeking to circumvent that resolution and would be spending that money for an improper purpose. If the EC could do that they could interfere with all decisions made by the OC at a GM.
You need to go back to a GM or individual owners should make an application to the CTTT.