Perella Weinberg's decision could swing the sale price of the 14 percent stake by almost $2 billion. It also may fuel the debate over the prospects for the brokerage industry. While firms are grappling with low market volumes and near-zero interest rates, new capital rules are increasing the attractiveness compared with riskier trading businesses.

There aren't many large retail brokerage deals for Perella to rely on. Merrill Lynch & Co., owner of the joint venture's largest direct competitor, sold itself to Bank of America Corp. in 2008 as it faced concerns about its survival during the financial crisis, driven by losses at its investment bank. Publicly traded firms such as Stifel Financial Corp. and Raymond James Financial Inc. are significantly smaller.

Proponents of the retail brokerage model, including Gorman, who ran Morgan Stanley's wealth-management unit before becoming CEO, point out the stable revenue and low capital requirements.

The division generated between $3 billion and $3.5 billion of revenue every quarter since the start of the joint venture, while the firm's investment bank swung between $2 billion and $6.4 billion. The company allocated $3.8 billion of Tier 1 common equity to the wealth-management unit last quarter, compared with $22.3 billion the investment bank commanded.

Wealth Management

Morgan Stanley's purchase of the joint venture has made it more dependent on wealth management. Revenue from that division accounted for 41 percent of the firm's total in 2011, up from 16 percent in 2006.

Matt Burnell at Wells Fargo & Co. is among analysts who say the business may have limited returns because financial advisers are paid on a pre-set scale that provides them with a larger percentage of revenue than bankers or traders receive and because the business is competing with larger banks and independent brokerages for a small number of wealthy clients.

Morgan Stanley's wealth-management unit has set aside at least 59 percent of revenue for pay every quarter since 2010, tried to cut costs as revenue dropped 2 percent in the first half and stopped setting targets that rely on an improvement in the markets. The firm's valuation of the joint venture implies an environment that isn't getting better soon.

"Volumes are at low levels, and there is the potential those levels won't increase materially in the intermediate term," Burnell said. "Most of these companies are trying very hard to get their cost structures as efficient as they can, but it is, by definition, a relatively tech-intense and personnel- intense business."

Cutting Compensation

Morgan Stanley has tried to cut compensation costs by reducing the number of brokers by more than 1,000 over the last year, raising the minimum amount of revenue an advisor must produce to avoid pay cuts and shrinking the number of trainees to 1,250 from 2,000. It is also attempting to boost revenue by offering more clients managed accounts that charge a fixed fee and pursuing customers who have more than $1 million in assets.