Help replacing '86 300E distributor cap - where does the O-ring go???
 

I bought some maintenance items for my wife's 86 300E, including a new set of wires, distributor rotor, distributor cap, and distributor cap O-ring seal.
When I removed the old cap last night, there was no O-ring anywhere.
The new O-ring I bought appears to be sized so as to fit in the bottom of deep circular groove on the mating face of the new cap. Is that where it goes? I'm concerned that in that location, it won't allow the cap to sit down all the way on the backing plate... does this matter?
As you can see, I'm a newbie at this. Any help would be appreciated.
Thanks!
Mika

it goes in that groove.

http://www.peachparts.com/shopforum/tech-help/102977-m103-oil-leak-burning-3.html?highlight=m103+leak

Pic 19 about 1/2 way down the page shows the O-ring on the phenolic cover behind the rotor.

I'm not sure I see pic 19... can you help me find it? I don't see it in the thread you mention...
Thanks!
Mika

I think this is it.

Thanks... but where's the O-ring? I don't see one in that pic...
Mika

The O-ring is around the outside of the outer extended ring and is visible in the pic as a black ring. It's used to keep dust and moisture from getting into the distributor cap and causing shorts. Look carefully at the pic.