I've read a lot here about the possibility of excessive crank case pressure. Do the breathers leak? Did it ever blow the dipstick out? If not why do we suspect it is excess crankcase pressure? Have you blocked the breathers and dipstick tube then added low air pressure to the crank case and watched the seal area with the engine not running? With this many seals it raises a few questions to me. Has the seal bridge been checked for proper alignment without the crank installed? Have the bridge mounting holes been opened up to allow the seal to center itself? Are the side seals pushing it off center? Is the seal bore concentric with the main bearing bore? Has the crank main seal area been checked for surface finish and cracks? My bet is many of these items haven't been addressed? Obliviously the engine assembler, not engine builder, hasn't done their job either.
Doug