It is a shame (on Porsche) that your fears are well founded.
Between the RMS and IMS issues that Porsche left unresolved for 9 years of so, the concern you have is quite valid when it comes to used Porsches.
Moreover, Porsche is quite variable when it comes to their warranty policies, which I know from bitter experience.
Too bad, in that a used boxster can be a very affordable purchase. It is the concern over the engine etc. that keeps me from buying one right now.
I would have no such concern over a used C4 or C5, all things being equal.
Now, if engine replacement/repair were more affordable, I would change my mind.
