helicoil for sure - I just went thru the same thing.
Only difference was I actually went to an auto parts store and got a new self tapping drain pug that was 17mm O.D. and had a smaller 10mm innner bolt. the outer threads were tapered and had thread sealer/locker on it and self threaded into place snug flat against the case bottom. it stays put and you simply remove the inner 10mm bolt to drain the oil. Pretty simple deal, really, I chose this because I could not find a 14mm (? cant remember for sure) helicoil that would have used the stock size drain plug.
Either way you need to drill out a bit more material for the oversized threads, so take your time, line up square and flush the case a few times with seafoam or similar to get all the chips out.