My nephew's pred90 had the same clanging in chain guard.We ended up taking the gaurd off because of we have trouble keeping the chain on.(see "shock" discussion )Also after a few motos the plastic(fenders,oil reservoir) are starting to show abuse.

 

if the bike has been stood up on the end it will leak some inj oil out.checkand make sure the cap is tight and you didn't over fill it.the boss you are talking about never had a bolt and there shoul be another one just above it with no bolt as well.if you trail ride don't remove the chain guard ,we went to the hardware and got some 1/4" plastic and riveted in the guard it still hits but no clanging ...

 

I took it back the were i got it and they just ordered a new tank and cap. But, i was thinking maybe it was leaking 'cause it was so full. I will check out the shock discussion. My son is about 50lbs. and the chain only makes that noise when he is on it. If i stroll around on it, it dosnt make that noise(the chain hitting the gaurd).