[right way right]

They don’t.
I was writing about the possibility of printing an engine more fully complete in what would be considered an essembled or nearly assembled unit by todays methods, thereby greatly reducing the amount of individual parts caused by the manufacturing process.
I’m writing about not having the need for separate heads, engine blocks, cranks, head gaskets, oil pan gaskets, bed plates etc. Its printed not assembled.
As it is today more Oil leaks on diesel engines are tolerated by consumers due to labor cost and frequency, so I was thinking more in that direction.

Being a tech my first thought is they would leak less but be less servicable
and more durable.

[uncommonsense]

"I was writing about the possibility of printing an engine more fully complete in what would be considered an essembled or nearly assembled unit by todays methods, thereby greatly reducing the amount of individual parts caused by the manufacturing process."

This is the most exciting part of "additive manufacturing"...

and your point about reducing serviceability (IMHO) will be mitigated by being able to "print" new parts, one-off, with impunity and added benefits.

I believe this technology will be most useful in creating medical devices or replacement body parts. I think especially when multiple materials can be laid down just like different colors in an inkjet printer.