I found the two different Banjos, 10mm and 12mm in my stock.....
and placed open wrenches next to them. The 10mm Banjo has a 17mm OD (on Right), the 12mm Banjo has a 19.8mm OD (on the Left).
This is the easiest way of determining the Check Valve size. A 17mm wrench slips over the 10mm Banjo. The 19mm wrench does not quite fit over the 12mm Banjo OD.
Whatever Pump & Check Valve you have, a replacement Feed hose to the Accumulator can be made up when needed.
If buying new Fuel lines AND new Pump, I strongly recommend going to the 12mm size. The early version 10mm Pumps are getting harder to find AND more costly. The later 12mm size are used everywhere, so more are made and easier to find and cheaper as well.
Hope this helps end the confusion. Even the Porsche dealers do not always know the differences.
Len