Hi All
Actually only crankcase pressure matters in the case of pushing oil seals. There are only a few of them, most are O-rings rather than standard seals.
1 the gearbox nose oil seal. This one has a cast in lip in the gearbox itself, it would take extreme pressure to move (crankcase pressure as there is no direct oil feed behind it)
2 the rear prop shaft oil seal on the crankcase side. Again this seal has a cast in lip by design. Sometimes it gets damaged on installation of the gearbox however that leads to seal leaks on the sealing lip. Often if not installed correctly it may weep on the crankcase parting line.
3 the oil seal on the water pump shaft. This can sometimes be seen as small oil drops coming out of the weepage bore holes below the water pump, normally not an issue.
4 the most common seal leak is the rear ignition seal on the crankshaft. If it is pushing out almost 100 % of the time this is a problem with high case pressure. If the leak is on the shaft to seal then it may be damage on the crankshaft itself with a wearing of the material from dirt and oil rubbing over very long periods of time. (such as a 2000 hour engine)
Checking the crankcase pressure on the ground as per the manual is done on a fully warmed up engine and at WOT. Be sure to check both the suction side and the pressure side. I note that you stated this was a recent overhaul. (?) Perhaps something was missed. In a factory overhaul all seals and O rings are replaced along with rings and crankshaft assembly. All bearings are changed and a lot of the parts reworked to the standards set out from the factory. Perhaps some information on where the leakage is might help..
Cheers
