If the price is right and the car is clean and seems to run and drive well, I would not be too concerned with the mileage. Try to get records and YES, YES, YES get at least a compression test. The reliability if leakdown tests is questionable, but definitely do compression.
At higher mileage you are closer to a rebuild than, oh...say...50,000 miles. But nonetheless, I have seen some SC's with far beyond 150K tha run great with good compression. Make sure the transmission shifts well (All 915's are notchy and balk at forced shifts), just make sure it goes thru all the gears and doesn't grind when going into gear. But difficulty getting into 1st or reverse (without grinding) can just be a clutch adjustment problem.
My best advice to you....take it to a good Porsche mechanic for a Pre Purchase Inspection (PPI), including compression test. Make sure it has Carrera style chain tensioners upgraded and a pop-off valve on the air box. If they have not been done..you need to do them soon. Tensioners ($500-800) and Pop-off valve ($50-100).
Good Luck...let us know how it goes.
Nick.
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Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com
PCA -- Rocky Mtn. Region
[This message has been edited by Nickshu (edited 06-07-2001).]