That must be something they came up with after my model year. For 19 years I've been doing it exactly the same way on this bike as per the genuine HD FSM. "Clean drain plug, install new o-ring, and tighten to 36-60 inch lbs." And it's always worked. Like I said, it's holding now so I'm not messing with it until the next fluid change! But yeah, pipe dope would probably work. I even considered teflon tape if I couldn't get it to stop.

 

...... During my career as an HVAC service tech I witnessed on several occasions that commercial plumbers use high quality pipe dope AND teflon tape. Their method is about 1 1/2 wraps of teflon tape around a male fitting and then lightly cover the whole thread surface with the pipe dope. I copied that whenever I needed to fit any pipe threads, and it always worked for me as well. The trick is not to use too much of either teflon tape or pipe dope.

 

If you install a new o-ring and install the plug hand tight you will feel the oring squeezing into the bevel. Once the plug is seated it should not leak.

Im not saying leave it hand tight and ride the bike. If you don't tighten it will fall out. If you turned a small o-ring boss plug a half turn after it seated the threads are damaged or the oring was pinched.