I have done 3 of these on my TD5, one was aftermarket, one second hand and one I just bought the regulator. The first included the main body to head gasket, the other gaskets I got of ebay.
The new regulator has been on for a few years now but I do have a pressure problem at start up, no power for a few seconds – not sure if this is related to the regulator or not, if I have less than a half tank of fuel I seem to get air in the system as well, but no leaks.
Reasonably easy to take FPR off, ¼ socket and drive and lie over the engine from nearside to get access.
There is a small O ring which I’ve never been able to see, confirm it’s existence or replace – I’ll leave this decision to you.
Trust you have a copy of RAVE