I once had a problem with the transmission
on my Yanmar
4JH3E with the Kanzaki
KM384 that resulted in silver colored shavings in my oil. This was due to an error with the throw and draw of my transmission cable that did not allow a full engaging of the gears. I would suggest that you carefully check to see if the gear
shift lever on the engine
is fully engaged in all positions by the action of the cable. Capt-couillon wisely refers to the other possibility of shavings comming from "shaft slop" and the suggestion of bushings. The brass color does represent another source of wear than the gears, but I don't have the knowledge to refer you to specific brass parts
in your transmission.