1999 Yamaha YZ400

I got this bike the other day and it just had the top end rebuilt. It only lacks needing oil and antifreeze to run. However, I went to put antifreeze in it and it started leaking from the pipe where it goes into the block around the gasket. Also, I'm not 100% sure but I think there was antifreeze possibly coming out the oil drain. This could have been from where the bike had previously blown. Any ideas on how to fix the leak at the pipe? I took it off and the o ring looks fine. 

Edited by swampkat18

There is no "block" on this engine.  Is it the water outlet pipe at the cylinder head, or the water inlet pipe at the water pump cover?

It's at the outlet pipe of the cylinder head

That has an O-ring seal.  Did you replace it?  If not, do so.  If so, you may need to remove the pipe and clean out any corrosion or other build-up you find there.   If it's clean and still leaking, you might need to apply either some #3 Permatex, or a Teflon pipe seal paste to it.

I replaced the o ring will find out tomorrow if it worked. Thanks so much for the help!

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