RE: I would note that many years and checks later, he changed his mind.
According to the wikipedia page you provided:
Brock now describes the book as a “character assassination” and has since “disavowed its premise”. He has also apologized to Hill. In his subsequent book, Blinded by the Right, Brock characterized himself as having been “a witting cog in the Republican sleaze machine.”
Why did he do that?
MONEY and Power, he became very unpopular with the Ruling Class immediately, maybe Ted Kennedy offered him a ride home after drinking one night. Either way I can guarantee you the numbers were sizeable. He may disavow his own writings, but the RESEARCH HE DID STILL STANDS.
Media whores screw whoever pays the most.