you remove oil cap and increase engine speed to 1500 or 1800 rpm, if blow slows down the engine is good, if it increases with engine speed then first ensure the breather system is not blocked, the valve clearances are correct and that the pump is timed correctly, incorrect pump timing will show as increased blow because the combustion pressure does not get into the back of the rings to seal the cylinder. It will also show up as increased oil consumption.
In extreme cases of bad valve clearances you will feel air being backed up into the airfilter - this also creates very horrible booming drone sound.
If everything is perfect and you still have blowby increasing with engine speed then your lower block is bad. Otherwise its just a simple tune up issue which most mechanics just say to overhaul because they dont know any better, their ustaads never taught them how to diagnose a diesel engine.
For hot start issue - check the pump timing, it either is stuck waaaay to advanced from a siezed cold start device or the pump is bolted too advanced.