D chunking:
http://www.lnengineering.com/boxster.html shows some images if you scroll fown.
Tip = yeah... $2500 is about fair. A local owner of a TIP Boxster had his fail and replacement numbers sound similar.
TIP = Automatic. Don't confuse with the PDK.
New Motor, New suspension certainly makes a stronger argument on a $19K, 100K+ mile car.
I think what generally annoys me about the M96 motors is that well, they just don't seem as reliable as the older cars. As such, I would be sure to have, available, to money on hand to deal with a potential motor failure. Just because your motor is "new" doesn't mean the same issues won't rear their head. Hopefully they wont and you will be one of a few with another 100K miles of trouble free driving.
Also curious about the history of this car.. yes, new motor, installed 5 years ago, but only 20K miles ago. This reaks of the very same issue you said about "only low mileage engines" seem to suffer. 4K miles/year seems low miles to me.