...perhaps one of the 'good looking' bushings may not be adequately performing their duty?
or perhaps, one of the replaced parts is faulty
never overlook the obvious....recheck and then look even closer
I find repeating this mantra and implementing it usually provides an end to the non-obvious/ fleeting issues
good luck and please let us know how things turn out
...have you signed into the 500e/e500 Roll call thread? search on 'roll call' if you'd like to be entered into the 500e roll call database of ownership