Since the tranny in inside the case halves and the tensioner is not, the metal piece from the tensioner would sink then flow into the small case holes down low. Chances are it's not a chunk stuck somewhere. The part(s) is probably in the oil muck on the bottom of the cases that never drains out.
ALSO..... the tranny is a constant mesh tranny. If something got into the gears, you would hear it in every gear since they are all moving. When I rebuild my engine (bought the bike with engine in pieces due to melted piston), I split the cases to clean up the small pieces of aluminum from the piston. There was only one or two tiny pieces in the gears and remember, the piston is in the same section of the case as the gears. The tensioner is not.
I would check the linkage adjustment. If I recall correctly, going into fifth was a tad bit more of a stretch/click to get in.
Check the cheap stuff first.As a FYI, the 5th gear, from the parts diagram (see tech section), is the second gear in from the output side of the tranny (far side of pict below).
Here's a pict I took when I had the cases apart.