<< guess on the amountof return of cap. on their past dist. >>
I can't give much help here. I understand that all of LINE's prior year distributions have been return of capital. At an earlier confernece call, Mr. Linn indicated that LINE will likely have an operating loss this year as well, which would mean tome that this year's distributions will be mostly return of capital. However, capital gains are reported separately from ROC and so you could have negative ordinary income (i.e., a loss) but taxable CG to report and pay taxes on.
For any holder, the allocations of gains and losses depend on units owned, the holding period of the units during a taxble year, and other factors like the MLP's income during your holding period.