Yep, lubed the O-ring (Sounds kinda perverted, don't it?
), then hand-tightened as far as I could, then wrenched it maybe 1/8 turn (maybe less). Felt nothing strip, heard no plastic cracking and seems to be holding oil.
It's a little tougher with the Boxster than in my other car (a Toyota), which one tightens til you feel the rubber ring touch the base, then tighten it another 3/4 of a turn. With the Boxster, I couldn't feel it suddenly giving more resistance as I got close to the end point---it just seemed to gradually give more and more resistance as I turned.
For anyone trying this for the first time with your Boxster, believe it when people say the oil really comes out fast. I've got a catch pan that's basically a self-enclosed container (I'm guessin' it holds maybe 15 quarts) and is fairly flat on the top, the surface angling gently down to the hole in the center. When the warm oil came gushing out, it hit that almost-flat surface and made a small wave that shot over the side of the collector. So even though I didn't have the disaster I had the first time I changed the oil, I still ended up spilling a bit onto the driveway (maybe 1/2 cup).
I've got an old metal funnel that I think I'm going to insert into the hole next time. I'm thinkin' that'll do the trick.
Thanks everyone for the input.