I thought it might be fun putting the new one in and I was right

The sensor had a tight fit in its hole, I filed the hole a little bit as I noticed some rust making things worse. I also stuck a git of grease around the hole to make things easier, maybe it might even help if I have to change it again someday

BoL suggest using a piece of string to feed it up through, this does work if you can actually get it through the top hole where the grommet would be so I put it underneath that around the top of the trailing arm and pulled it up until it couldn't get through the gap between where the grommet will be and the trailing arm. I found that if I then pulled it back out a bit, it then got caught in the grommet hole. A couple of minutes tinkering with a pair of normal long nose pliers, and a foot long pair of pliers I bought thinking "What am I ever going to use these for?!" allowed me to pull the connector up through. You want to then get the piece of string over by the exhaust back box to make things easier later on.
The hardest bit is now trying to get the grommet home, access is very limited due to the gap between the top of the trailing arm and the bit of metal on top, and generally all the metal around the arm. After much tinkering and thinking I found the best way of getting it at least parallel to the grommet hole, was to jack up the trailing arm and get the grommet as near as I could get it to the hole, on a diagonal. Then let the trolley jack down, therefore letting the top of the trailing arm 'grab' the grommet and push it level to the hole.
I then spent a good while trying to get the grommet into the hole with very little success, so out came the foot long pliers straight up underneath the 'top trailing arm housing' (to think of a better word), and push it so the grommet is above the grommet hole, now is a good time to get a bit more of the sensor wire through the hole to make it easier to plug it into the loom.
The best place to plug this in is from underneath the car by the exhaust back box, this is incidentally where I unplugged the sensor to remove it originally, so the loom wire was still here. The new sensor plug has probably tucked itself somewhere awkward, this is where the bit of string then comes in handy again, just a case of pulling the plug over to you


Back to the 'outside' of the car again to pop the grommet back down into its hole, I found that my pair of pliers or maybe a pair of right angle circlip pliers can be used to push the grommet back down on one side, then twist it around using pliers to do the other side and twisting back so nothing's under tension.
Generally, if in doubt, try looking at it from another angle, literally. Its suprising what extra gaps/better ways of doing it you find. For example, that 'tiny' gap where the sensor plug to loom connection is a lot easier coming from under the car, maybe even with a carefully placed mirror. Just take your time, don't pull the sensor cable too hard for one its a lot of money!
