Hi, I have removed distributer put a new O ring on and O ring seems too small for the groove it sits in, anyway I reinstalled distributer and it is still leaking

 

Buy it from the dealer, it's like a couple of dollars, aftermarket seals are junk.

 

Heck if it's over 2 dollars I would be amazed. It is a very snug fit when a new Honda o-ring is used, like you actually have to lube the ring with a drop of oil to get pop it back in all the way.

Also check the cam cap for the other cam, and if an H22, check that the vtec solenoid isn't leaking.