It has been widely reported that General Motors (GM) is considering selling a huge stake in its financing division, GMAC, in an attempt to sure up its finances. With net income of $2.5 billion expected this year, GMAC is worth somewhere in the $30 billion range, so a majority stake would yield the leading domestic automaker a substantial sum of $15 billion.

What's interesting is GM's current value. At $28 per share, Wall Street is valuing the entire company at $16 billion. In essence, GM's car business has an implied value of negative $14 billion. GMAC itself, therefore, is worth nearly $60 per share.

Maybe GM should try and sell a stake in its auto division, not GMAC. Such a move would substantiate a positive dollar value for the car business, and maybe get the stock price up. If GM could ever sell cars and trucks for a profit consistently, you can see why value investors like Kirk Kerkorian think the upside is tremendous.

Selling GMAC, though, could backfire if the $15 billion generated slowly disappears. Right now GMAC is the life support for GM. Perhaps that's something they should hold on to in its entirety.