As other folk have mentioned, your leak might not even be the rear main seal. Any oil leaks up in the valley of the engine will drip down the back - looking like a RMS. Check up there first for any oil. Could be turbo pedestal, HPOP, high pressure oil fitting... Also could be a leak at the rear of the oil pan.
That being said, I had to do the RMS on my T444e a couple weeks ago. Had to pop off the 5-speed Spicer manual transmission which was heavy, but otherwise trivial. Clutch and flywheel came off easy.
With those removed I could see that the RMS was weeping. Also, the rear plate was leaking in a couple places. Popped it off, cleaned it up, put on some fresh Permatex "The Right Stuff" and reinstalled. Installing the new RMS was easier than I thought. Firstly do not separate the seal from the wear ring
! You do not want to oil between the wear ring and the seal. It's Teflon and should not be pre-oiled.
I did put some thread locker on the inside surface of the wear ring. There is a special Loctite product for this application. I couldn't find it anywhere.
To install the new RMS I used the flywheel torque plate that came off with the flywheel. Looks something like this:
With 3 bolts evenly spaced I tightened them up incrementally to walk the wear ring in place. Used a micrometer against the bolts to make sure I was pushing evenly. Smooth and easy.
I really wish I took some pictures. I'd have loved to share it with everyone.