Hey Scott

the plastic collar does the same thing as the fuel tubing, so that in an of itself won't cause the problem.

I gather you got this second hand, so you probably can't be sure about its crash history.

Make sure the spindle is straight and not bent. Check each bearing individually to make sure it is smooth with no notchy spots. If any are, replace them.

Look at the blade arms to make sure they are straight (if plastic not cracked) and look at each mixer on the blade arms to make sure they are straight. Last time I had this problem it was because one of the mixers was bent.