Asset Sale Limitation - Withdrawal Liability - Section 4225(a)

I have a client that is a closely held business that sold all of its business assets related to its union business and was assessed withdrawal liability by a pension fund.  We argued that the asset sale limitation under Section 4225(a) limited the assessment to 30% of the company's liquidation or dissolution value.  The fund is taking the position that the company is not entitled to this limitation because it did not sell "all or substantially all of its assets" as required by Section 4225(a).  Of course, the company did not sell its cash and A/R but also did not sell its minority stock ownership in a different closely held company (it would be very difficult to sell this minority interest to anyone).  Based on this, the Fund is saying that since Section 4225(a) on its face requires a sale of "all or substantially all of the assets," the limitation does not apply.  If the company had sold its minority stock interest in the other company it would have sold more than 85% of all its assets.  Even without this stock sale, the company did sell 100% of its operating business assets.  I have researched this and could only find one older arbitration case where the arbitrator held that non-operating business assets should be excluded in determining whether all or substantially all of the company's assets have been sold.  Does anyone have any experience with this?  Thanks in advance.   

No but if the fund still pushes back, initiate arbitration and cite the case to the arbitrator.