Low coolant / bad cap? / flashing light above 250

[husker boxster]

The antifreeze isn't a matter of having to use Porsche brand (although some will insist you do), it's a matter of using a phosphate-free antifreeze. Your garden variety brands contain phosphates and if you add it to a system that requires phosphate-free antifreeze you will generate a nice gell in your system that will halt any flow. Many European cars, not just Porsches, require phosphate-free anitfreeze.

Also be aware there are early and late types of phosphate-free antifreeze for European cars. Zerez makes a brand in a gold bottle (I think it's called M30) that is designed for Porsches up to 1995. Obviously that won't work with your Box.

Haveline Extended Life (Dex-Cool) antifreeze will do the job.