I would be almost willing to bet that it was the timing cover leaking rather than the chain tensioner plug.

The timing cover can leak from the extreme end where it mates up against the head.
I bought a timing cover gasket at the dealership - it was a Victor Reinz. The new gasket wouldn't let the cover mate up to the head properly and there was a small leak - very hard to see. I ended up having to do the job again - paring the gasket slightly to get the cover to fit exactly.