distributor o-ring ?

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how big is this o-ring the one the dealer gave me is for a 3" diameter something it seems to big i dont want to remove my distributor without verifying i have the right one as i have a oil leak and dont want to make it worse
honda part number would be appreciated , running the forum search is giving me vague results
the part number of the o-ring they sold me is 30110-PE2-901 and there is a smaller number on it as well D4E27 this is on the red and white label.
thanks for your input.
ok i have found on the site the one they gave me wa snumber 8 so i guess i have to get the smaller one too. number 7. there is alink around here somewhere where you can order them the illustration from the hondas book lists number 7 as ill.# 4459
so i guess i can buy that one too as it is small and fits on the shaft.
http://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=Accord&catcgry2=1986&catcgry3=4DR+LXI&catcgry4=KA5MT&catcgry5=DISTRIBUTOR+%28PGM-FI%29+%28TEC%29

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the 3" still seems too big
boy this is going to be fun!, after further review of the link i was looking at wrong distrib. but number 7 is still correct the 4459 o-ring now i have to take this other one back as it is mystery o-ring.