Update - I bought a new sensor and it seems to be working so far.
I tried RockAuto as suggested (thanks JeanLuke), but there were no available parts on the Sprinter. After emailing and calling around several Jeep and Merc dealerships, the best I received was a quote for $2984.01 + GST for a new rail which includes the sensor
. So I messaged Hi Tech Diesel from Adelaide, who sold me my new injector, and they were friendly and helpful and quoted me $340 inc shipping/gst for a new sensor.
Anyway - here's a photo of the old sensor (top) and new sensor (bottom). The new sensor is a bit shorter and the manual says it replaces the old sensor. The new sensor part number is F 00R 004 269, and my old sensor was 0 281 002 498.
Following is some data I logged from WJDiag which visualises the previous intermittent fault. You can see that the sensor periodically drops out (voltage drops to near zero - short circuit). My guess at what the problem was is that when the sensor resumed working it would momentarily read a very high voltage, which the engine would interpret as too much rail pressure causing it to drop fuel which caused the engine to almost stall (and in some cases stall).
Anyway, hopefully that fixes that. We'll see. I'll update this thread as I go.