The oil samples typically show wear metal however if there is a catastrophic failure large chunks of metal will accumulate at the bottom of the pan and in the filter apparently the filter looked good? Are you sure the breather tube going from the PCV to the intake is clear? If the engine can be run enough for a cut out test you may be able to narrow down a cylinder to look at. We had a combine delivered last year and it was 20 below out they let the machine sit on the trailer in the shop overnight and started it the next day. They ran it outside and were hooking up the trailer to move it out and during that time the PCV valve froze up. They went to move the combine back in, throttled it up, and the entire valve cover blew up due to the pressure in the crank case, it made a huge mess. I don't know how much oil would get flung out of the back of the engine with all the gears rotating and the cover blown off but I would have to think it would be a pretty good amount. I guess I would hook up the manometer with a new PCV cover and filter and start the machine, monitor the pressure, and if it is way high at idle something is seriously wrong. Then I would raise the RPM and monitor until your at high idle. If it's still under spec run it under load and watch it then record what you get. At the end of this remove the PCV filter and see if it's saturated in oil it should not be after running this little. If the PCV system is not blocked and the crankcase pressure is within spec like the shop said it is you will not blow another cover. If the crankcase pressure is high and the breather system is clear and functional it's time to start looking into it maybe the rings are shot or the cylinders are glazed and allowing combustion pressure into the crankcase. How many hours on the machine?