The splash-flush method with the solvent will clean the crankcase far better than you'll ever be able to do with a brush. Do you clean your clothes with a brush before putting them in the washing machine? No, the pan gasket won't be re-usable unless it's only been on there a matter of hours or days- - - - -certainly not decades! The crud in the pan will get dislodged, emulsified, and drained with the hot oil after the flushing is done. The engine will end up cleaner that way than it's been in years. It also might spring a few oil leaks, because some of them only hold oil because the oil can't make its way to worn or damaged gaskets through the sludge! Be prepared to replace things like the valve cover gasket, side cover, and possibly the rear oil seal.
Jerry
