I doubt that any of the rubber oil hoses will have 3-4 bar pressure in them Herrie. The Suction hose is drawing oil from the tank to supply the oil pump, so lower. The Return hose is scavenging oil from the sump to return it to the tank and will be about tank pressure. The air vent at the top of the tank is vented into the crankcase, so will be a a similar pressure. The crankcase is vented, via restrictor and into the throttle body and then to atmosphere, or inlet pressure. Not sure what pressure the crankcase runs at but it won't be much if vented to atmosphere.
Agree that good quality hose clamps are certainly recommended, the pipes they fix on to are mostly not serrated and any hose coming loose will be very bad for engine life!
Most leak down compression testers do give ways of checking various parts of the engine, such as squirting some oil into the cylinder bore to test for faulty piston rings. I suppose you have checked closely for leaks though rcmatt? If the engine was burning that amount of oil it would show up as blue smoke. The base gasket of the cylinders often leak and causes a fine mist leak that isn't that easy to locate.
