It's almost a rite of South Korean politics: As a president's single five-year term nears its end, a feeding frenzy of aggressive corruption allegations begins.

With four months left in office, President Lee Myung-bak, who campaigned on an anti-corruption platform, is watching his only son and an elder brother come under fire for alleged irregularities in funding Lee's retirement home. Another brother was arrested on separate allegations he took bribes from bankers.

Corruption has dropped since South Korea achieved democracy in the late 1980s, after decades of military-backed rule, but it is still a problem in business, politics and elsewhere.

Nearly every former South Korean president or their family members and key aides have been embroiled in corruption scandals at the close of their terms or after leaving office.

Even late President Kim Dae-jung, a Nobel Peace Prize laureate and champion of human rights and democracy, was forced to repeatedly apologize after his sons, relatives and high-ranking officials were implicated in corruption allegations.

On Thursday, special prosecutors summoned Lee's son, Lee Si-hyung, for questioning over a now scrapped deal to buy land for Lee's retirement home. Lee Si-hyung bought part of the land. The presidential security service bought another part in order to build facilities that the government provides to protect ex-presidents.

Opposition lawmakers allege the son received a sweetheart deal that allowed him to pay less than market value because the security service overpaid.

South Korean special prosecutors also raided the home of Lee's brother, Lee Sang-eun, as part of the retirement home investigation. Lee's office denies allegations of wrongdoing, saying the land was bought for a fair price.

The land controversy and other corruption allegations have been an embarrassment to the ruling party as jostling ahead of December elections heats up. Lee's term ends in February.

Conservative ruling party candidate Park Geun-hye is facing two main opponents. She leads in many polls, but analysts believe the race could turn around should the two main opposition figures unite.

Controversy dogs many presidents in their closing days in office. Lee's predecessor, Roh Moo-hyun, committed suicide in 2009, a year after leaving the presidential Blue House, amid allegations his family members took bribes in exchange for their influence.

Lee pardoned Roh's older brother, Roh Gun-pyeong, who was convicted and sentenced in 2009 to two and a half years in prison for influence-peddling while his brother was president in 2006.

Another Lee brother, Lee Sang-deuk, was arrested in July after a court approved a warrant on allegations he took half a million dollars in bribes from two detained bankers with the intent of using his influence to help the bankers avoid punishment. Enraged protesters threw eggs at the brother, grabbing his tie and jostling him as he entered court.

President Lee apologized after his brother's arrest, calling recent corruption scandals involving family and aides "heartbreaking."