Dozens of members of the Bareun party splintered from the main conservative group, then known as Saenuri, as accusations mounted against Park and joined forces with then opposition lawmakers to vote for her impeachment.
The ousted president is now on trial for corruption and other offences.
But the Bareun party's own leader Lee Hye-Hoon has been under increasing pressure since prosecutors last month opened an investigation into allegations a businesswoman gave her cash and gifts worth about USD 50,000 over nearly a dozen occasions.
She insisted she would clear her name and "the truth will come out sooner or later".
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Lee took the helm of Bareun -- or "Justice" -- in June, after the government changed hands with the election of liberal president Moon Jae-In.
She vowed to make Bareun the "main base" of conservatism rather than Park's party, now renamed Liberty Korea, but the allegations undermined those efforts.
Yonhap news agency said the scandal dealt a "major blow" to the party's drive for "new, transparent and warm" conservatism.