little rubber plug inside output flange

[sik8v@netscape.net (rhys)]

well, got the car up on the hoist...good news! the oil smell wasnt gear 
oil, but cv grease spitting out of the split boot and hitting the 
exhaust manifold (smelly!)  the new axles have been on for about 1000km 
so i got a replacement axle for free. score.

but...i did find something weird.

the little rubber cap in the middle of the output flange was gone. it 
was about the size of a dime as compared to the original size of a 
toonie (yea yeah, im from canadia :p ). and there was also what looked 
like it used to be a washer, again about the size of a dime and the 
thickness of a peice of paper. they were just sitting around in the 
flange and the CV grease was full of metal shavings and rubber 
chunks...WTF? obviously they fell off and got destroyed by the cv, but 
how, why?

now theres a threaded hole exposed (i assume for the puller when taking 
flanges off)  can anyone tell me where to get another little rubber 
thing/how it goes on/what it does/if any damage could have been caused?

THANKS,
Rhys