The rear side panels are screwed in.
If I properly remember starting at the back, you also need to pull the hatch rubber-gasket.
May also need to remove:
Door sill cover in order to remove the vertical cover along the rear hatch post (L/R)
Then the vertical cover on the rearmost pillar in order not to break the plastic. (along window vertical)
I think there were a few small round caps which had to be pulled using a small screwdriver.
You have to remove the covers and look inside.
Put the rear seat down to access two or three along the bottom.
Under the carpet as well if i properly remember.
The book says it is a two-piece molding over the wheel wells, split about where the backrest of the rear seats is. I think mine was a single piece which was the reason I had to unscrew to the bottom of the rear passenger compartment to remove the side trim.

If you want to remove the whole side covers:
May need to remove the seatbelt bolt (large Torx T45 or T50) to completely remove the panel.

In any case - It is screwed in, so pull gently to locate attachment points, but it cannot be pulled away!

As for the temp sender - I'll head to the garage tonight, been abroad for a week.

 

thx already for this usefull information

 

Still due with an answer to the temp sender unit.

Couldn't find a second sensor. Book also says only one.

Had the red overheat show 21 years ago. So memory may has let me down on the two sensors.

So changing the one sensor should get a valid temp signal.
But then the digital clusters can fail in funny ways.

 

Right cylinder head should have the temp sensor for gauge. The one by the water inlet is for the ECU. There are 2 different sensors for the dash depending on if your dash has a gauge or a idiot light. The sensor in the head is a one wire sensor and the one by the water inlet is a 2 wire sensor.