daihatsu terios distributor o-ring size

I had to change my o-ring on the distributor, however I couldn't get the right size. I use one that was close in size, but still got some leaks. My problem is i forgot where I place the paper I wrote the original size on. HELP! I'm in Barbados where you cant find available parts for certain cars. HELP! I need the correct size for my distributor seal.