the more you think
you know about them, the less you seem to do!
But since they have not come back, just smile alot!
The banana plugs are good for cars that have the 8 and 16 pin Diag Connector but your 500SEL has the 38pin. Thus you need small pins that mate with the female pins in the connector. This is not news to you since you've already figured this out.
But BE CAREFUL, since you could
do damage plugging into that connector by mis-plugging, shorting adjacent pins, etc..
described on my page (menu#2) at the bottom, is the safest
way to interface the 38pin diag connector but they cost about $200, so there goes the money savings! Difficult problem!