I would just pick up a used HPU; that way you’ll have other parts in case it’s not the pressure sensor. In fact, I would purchase both units HPU and GSA. Guys doing the conversion to regular manual sell them cheap.
Pry around the nub on the left side in your picture using a small screwdriver. If it breaks the latch it’s no big deal. I’ve not had them jump apart with a broken latch. If you’re still stuck I’ll try to get you a good picture.
It couldn’t be easier than the situation you have, assuming it’s the pressure sensor. You don’t need to remove the HPU, just simply unscrew the sensor and screw the new one in.
Edit: do this when there isn’t hydraulic pressure built up in the system.
So, I'm currently unsure of what to do in my current scenario. My 2003 SMT Spyder recently decided it was going to stop shifting out of neutral... but only intermittently. I noticed when I opened my driver's side door- the HPU didn't seem to turn on as you couldn't hear it at all. However...
If you read carefully through this thread, it sounds similar to your “run times” , where replacing the pressure sensor fixed it. Also, the author says the pressure sensor can be purchased through MWR.