Reading this thread reminded me of BIGjake's "IMS failure" that turned out to be alternator and serpentine belt.
BIGJakes (ims?) dilemma
Not to get darkstormvx's hopes up too much, but there are a few problems that will stop the engine, but not cause catastrophic damage. At >200K miles I can think of a few parts that could be worn out.
+1 for looking for another shop. Sounds like you know your area, but ask here if you haven't already looked:
Find your local mechanic/porsche specialist
And like others have mentioned or implied, If there is significant (metallic) debris in the filter, any attempt to repair the engine will not be cost effective. Once the IMSB has failed, you do not replace the IMSB.