After 40 years the records have been released, ostensibly to, “help end allegations of behind-the-scene deals.” While that is an issue, the issue that likely was more compelling to the ROK government is Tokdo (Dokdo)/Takeshima:

The allegation that Seoul yielded the Dokdo islets to Tokyo to use as leverage for the talks was found to be groundless. The 35,354 pages of documents proved that Tokyo laid claim to sovereignty over Dokdo throughout the normalization talks, but Seoul made it clear that it could not yield its territory to Japan… The documents also showed that one of the Japanese negotiators proposed to blow up the Dokdo islets to remove the source of a territorial dispute between the neighbors.

North Korea is expecting a windfall of reparations when it finds a way to normalize relations with Japan as well, to the tune of 10-12 billion dollars, and so will also likely closely study the documents:

Of special note is the government’s attempt to raise property claims against Japan for those residing in the northern half of the Korean Peninsula, citing its status as the only legitimate government on the peninsula. However, Japan rejected the demand and insisted on North Korea’s right to assert the claims of its government and North Korean nationals to properties in Japan, which remain unsettled.