American International Group Inc, the world’s biggest insurer, has announced it will replace CEO Martin Sullivan. The news comes after AIG reported record losses due to risky mortgage bets.

Sullivan follows the departure of a wave of Wall Street top execs, including the recent bloodletting at ailing investment bank Lehman Brothers.

“On Wall Street, after Bear Stearns fainted, the other financial firms took smelling salts,” says Bill Bonner in The Daily Reckoning.

But some of them are beginning to look a little woozy, nevertheless. Lehman Bros. is said to be looking for $3 to $4 billion in new capital. The company has nine times as much in level 2 and level 3 assets as it has in tangible equity. And it’s not the worst. Merrill Lynch’s level 2 and level 3 assets equal 2,565% of its tangible equity.

And dear readers, be aware: “There’s another Bear Stearns out there,” say our friends over at The Motley Fool. “You may already own it. And just as with Bear Stearns, chances are you won’t see the collapse coming until it’s too late.”

Colleague Dan Amoss, over at Strategic Short Report, has pinpointed the next Bear Stearns – and warns that there is another credit crisis ready to jam the pipeline.

“Right now,” he tells us, “this company is desperately scrambling to dump more of its weak, illiquid assets…while laying off employees by the thousands…in a desperate bid to ‘fix’ its Wall Street profile, keep its ’shameful secret’ under wraps, and protect its stock.”

But that won’t work, Dan continues. “Buried deep in this firm’s mysterious ‘Level 3′ assets, where banks have regularly hid their riskiest mortgage-backed securities, this one company already has one very large multibillion-dollar real-estate-based asset that – just by itself – could be worth nearly 30% less than it was when this firm bought it.

“When this firm is forced to beef up earnings by selling this one asset, you’re already looking at billions in write-down losses right there. And that’s just where the unraveling begins.”

“Don’t buy shares of financial service companies with ‘Level 3′ assets of more than their capital,” says Martin Hutchinson in Money Morning.

That’s all the “Big Four” investment banks including Goldman Sachs, Merrill Lynch & Co. Inc. (MER), Morgan Stanley (MS) and Lehman Bros. Holdings Inc. (LEH), and most of the big commercial banks, too. Those Level 3 assets are probably worth very little in a real downturn, because there is no market for the assets and everybody else will be trying to sell them too.