If the engine is running that hot, you should notice the gauge reading being high.

Underhood temps have been high in diesels the last few years, it causes all sorts of problems like you are seeing.

You can get some cheaper DOT 4 fluid. The Porsche stuff may have a higher boiling point but I doubt for the money it is worth it value wise. All the DOT 4 fluids have a higher boiling point than the lower numbers so even a cheaper one will have better results than what you are running now.