Ok, so here is my guide to repalcing the FSU/FSR on a right hand drive 1998 e39.
Step 1: Remove the following panel:
To do that you need to firth remove the screw found here:
After that, just slide the panel towards the back of the car to remove it.
Step 2: Remove the indicated panel by undoing the indicated fasteners. Please note that the two hex drives.
With the 2 panels removed, you will now have access to the cavity where the FSU resides. It is VERY tight in there.
Step 3: Detach the FSU cable, by squeezing the indicated tabs together and wriggling the cable lose
Step 4: THE HARD PART! Remove the FSU by simultaneously pushing down on the indicated tab and pulling on the FSU
Now reverse the process when putting the new one in.