[Ronzi]

Just from a wear standpoint, there is no reason to believe the engine would be worn out any more than a 100,000 mile Miata. Typically, late model Porsche engines should be pretty long-lived, a couple hundred K at least.
As said, if at all possible, take it to a dealer for a PPI. They can pull up the warranty history from the VIN, and at least be able to tell you if an engine has been replaced under warranty. My assumption here is that there are no maint. records with the car.
Some of our forum members have said the RMS is a "wear" item, and can be expected to fail eventually on every engine. Once the RMS makes it past the premature failure period, how long with it last? I haven't seen any evidence that would lead me to believe anybody knows.
If the car has been maintained properly during it's 100k miles, it could be a decent buy. If not, it could be a disaster waiting to happen ... to you.
The used car world does not seem to me to be short of Boxsters, so you might think about passing on this one, particularly if it has known needs, and look for a better car.