Hyundai Mobis Corp., the vast automotive parts and systems producer whose president, Chung Eui-sun, became a vice chairman of Hyundai Motor Co. Ltd. last week, today acquires an additional 5.83% stake in Hyundai Motor, increasing its ownership to 20.78%.

The transaction is causing analysts to take a closer look at shareholdings and management structure at several of the companies within the Hyundai-Kia Automotive Group, in which the Chung family holds various ownership positions.

The analysts are on the alert for possible clues to overall strategies at play within the group, which are often elusive and clouded by complex interrelations.

Hyundai Mobis acquired 12,854,195 shares of the Hyundai Motor stock for an acquisition price of 1.37 trillion won ($1.1 billion) from Hyundai Steel Co. Ltd., which is owned 12.25% by Chung Eui-sun’s father, Chung Mong-koo.

Chung Mong-koo is chairman of the board of Hyundai Steel and chairman of the board of Hyundai Mobis and holds 7.74% of the company.

Kia has a 17.76% stake in Mobis, and Hyundai Steel controls 6.28%.

The elder Chung rapidly grew Hyundai Steel into Korea’s second-largest steel producer through several highly successful acquisitions and mergers.

Kia, in which the younger Chung is a shareholder and was until last week president, controls 21.29% of Hyundai Steel.

Chung Eui-sun’s holdings are not listed in generally available corporate information for either Hyundai Mobis or Kia, but the younger Chung, 38, is ranked as the eighth-richest shareholder in Korea, based on the value of shares held in his personal portfolio.

In 2008, his holdings of 1.303 trillion shares of publicly traded stock were valued at $765 million, according to Forbes magazine.

Adding to the analytical intrigue of those trying to unravel the inter-corporate shuffles in ownership and executive responsibilities is the fact the vice chairman and CEO of Hyundai Mobis is Kim Dong-jin.

Up to this year, Kim was the vice chairman and principle co-CEO of Hyundai Motor, as well as the right-hand man of Chairman Chung Mong-koo. Kim ran Hyundai Motor as its CEO for two months in 2006 when Chung Mong-koo was incarcerated on charges of embezzlement.

Kim was a co-defendant in the case but not imprisoned while awaiting trial. Like Chung, Kim received a suspended sentence for his alleged role in the affair.

In July, Kim announced a vigorous growth plan for Mobis to invest 1.2 trillion won ($965 million) by 2025 in an effort to double annual sales from 11 trillion won ($8.8 billion) currently to 22 trillion won ($1.76 trillion). Kim also stipulated Mobis would increase core-parts sales to account for 50% of total deliveries, up from 30% at present.