i'm not a big fan of PPIs. i know that flies in the face of common wisdom, but i have a rather unique perspective on this.
when you take a car to a shop for a
PPI, if they think they might get the work, they might be motivated to find things. however, they may only find the things that will profit them. i've seen a bunch of shops say the trans needs a rebuild, when it was just fine.
if they are told they aren't going to get the work, they may not find anything, as they are not motivated.
the bottom line is that if you want to have somebody look at the car, that's fine. however, it needs to be a shop that does 968s, and not just 944s. further, it needs to be a shop you have a relationship with. otherwise, how will you know if they are telling you the truth?
also, a compression and leak down test should be done, as well as a variocam inspection. most shops won't do that, and without it, you really have no idea what's going on inside the single most expensive part of the car. any idiot can look at brakes and suspension. you don't need to pay a shop to do that. nobody but a shop who has experience with these transmissions can diagnose that part, and even then unless it's making noise, they won't find anything, and you would have already deduced there is a problem if there was noise, thereby doing that part for them.
that leaves very little for a shop to do in a traditional
PPI. none of that will get done for $100 either.