I don't know that engine or system, but if there are very thin copper washers, that look like copper "foil" ?
Those would be common "crush washers" which literally ARE copper foil. They are intended to distrot and conform to the shape of the joint they are sealing, and most folks are unaware that they are strictly "use once and replace" parts. REPLACEMENT IS MANDATORY. They will plague you with fuel or air leaks if you try to re-use them, so if your system does use them, order a box of a DOZEN so you have no incentive to re-use them. In many systems you would bleed air from the lines at these some points--and the process of loosening the line and then tightening it (bleeding) actually requires replacing the damned crush washer, or it will leak.
This is one reason why some of us will share quarters with a diesel engine, but we'll never love it.