Keg O-rings.
 

Here are the O ring numbers for the corny kegs I have. I would assume that they are standard to all cornys. However I cannot find the right one for the lid seal Does any one know what it is supposed to be?

O-rings on the ball lock (outside on the connector)
#9 o-ring 5/8 x 7/16 x 3/32

O-rings on the down tubes(inside and underneath the valve assembly)
#83 o-ring 1/2 x 5/16 x 3/32

O-ring for the lid seal.
? Any one know? I think it has an I.D. of 3 1/2 inch and a thickness of 1/4 inch but I cant find it.

Keg "O" Rings
 

My homebrew shop sells these o rings check out
http://www.homebrewing.org/msg3.htm
They will ship too. They also sell kegs (used) for about $14.99 I think.
Of course you'd have to pay shipping ( the unavoidable)

This may help you out.

http://www.williamsbrewing.com/KEG_LID_SEALING_O_RING_P58C78.cfm

Yeah i've seen the kits out there. I just dont want to pay for something that i can easly get my self for 20 times the price. The o- rings fot the other parts that i did find were 25 cents a piece and i did not have to pay shipping.

3 1/2 id looks good, by measuring around the seat.

Inlet and out let are different diameters, measure both. Also, inside each valve is another one...there is a total of 7 per keg?

Just got the specs from The cornelious company. The lisd o-ring is 3.47 ID with a 0.275 cross section. Their part number is 180362000. If you go on to their parts supplier www.bevcore.com and search for that part number it will come up. I ordered 5 and there was a volume discount, about 1.90 a piece.

I did not notice that there was a diffrence in the o- ring size for the inlet and the outlet. I dont think there is on a ball lock. I know the inlet and outlet are keyed to different sizes so you dont hook them up wrong. There is an o ring on the down tubes and around the outside of the inlet and outlet. I dont think you can replace the seals on the spring loaded seals, you just have to replace the whole spring assembly.

I thunk I heard that you just push the valve out the bottom, after unscrewing the valve from the tank. Then, replace an o-ring. Last time I needed a big o-ring, about 4 1/2 inch, it was 75 cents at the local chain/bearing/power transmission products store. Tractor supply? Ace hardware?