By Erik Holm Of DOW JONES NEWSWIRES NEW YORK -(Dow Jones)- David Sokol, the Berkshire Hathaway Inc. (BRKA, BRKB) executive who resigned last month, had more conversations with bankers for Lubrizol Corp. (LZ) than previously disclosed, according to a regulatory filing that adds more detail about the chemical maker's interest in a potential deal. Sokol was told by the bankers on Dec. 17 that Lubrizol's chief executive planned to discuss Berkshire's possible interest in a takeover with his board of directors, according to the filing released late Monday. The new information in Lubrizol's proxy filing for shareholders adds to the timeline of events surrounding Sokol's trading of Lubrizol shares in his personal account in December and January--a purchase disclosed by Berkshire Chief Executive Warren Buffett on March 30 when he announced Sokol was stepping down. Sokol had been widely seen as a leading contender to succeed the aging billionaire at the helm of the Omaha insurance and industrial conglomerate, one of the biggest U.S. companies. In his announcement last month, Buffett said the resignation was Sokol's choice but noted that, unlike past instances where Sokol contemplated leaving, he didn't try to stop him from resigning. Sokol first discussed his interest in Lubrizol with bankers on Dec. 13. A previous version of the proxy, filed with regulators before Sokol resigned, hadn't indicated whether Sokol was aware that Lubrizol was taking that interest seriously. The updated version shows that the bankers agreed in a Dec. 17 phone call with Lubrizol Chief Executive James Hambrick to inform Sokol that Lubrizol's board would be told of Berkshire's interest. Sokol was told as such that same day. By then, Sokol had already purchased 2,300 shares of Lubrizol, according to Buffett's March 30 statement. He sold the holding Dec. 21, only to buy 96,060 shares from Jan. 5-7 for about $10 million. Berkshire reached a $9 billion deal to acquire the company in mid-March, boosting the value of Sokol's stake by about $3 million. The updated filing added that Hambrick requested that the bankers act as a go-between a second time "on or about Jan. 10" to inform Sokol that Hambrick would be contacting him directly. The filing noted that the bankers conveyed this information to Sokol. Buffett revealed in his March 30 statement that Sokol approached him about a week after taking his second stake in Lubrizol to suggest that Berkshire buy the company outright. Buffett said that Sokol mentioned at that mid-January meeting that he owned Lubrizol shares. Buffett characterized the comment as "a passing remark" and said he didn't press for details about the date of the purchase. Sokol has said he believes he did nothing wrong in making the trades and they weren't a factor in his decision to resign. Neither he nor Buffett immediately responded to requests for comment late Monday. People familiar with the matter said last week that the U.S. Securities and Exchange Commission is looking into whether Sokol's purchases of Lubrizol shares violated insider trading or other securities laws. An independent committee of the conglomerate's board will also be reviewing the transaction and Sokol's trades to determine whether there was a violation of the trading policy, a person familiar with the matter said last week. Lubrizol also said it will hold a shareholder meeting to vote on the Berkshire deal on June 9. -By Erik Holm, Dow Jones Newswires; 212-416-2892; firstname.lastname@example.org --Leslie Scism contributed to this article.