There seems to be a bit of debate as to if you should lubricate new oil seals before fitment, what is the current school of thought on this?

I am about to replace the large output oil seal on my '84 K100RS and want/need to get it right.

With a new OEM you should soak them in engine oil for 2 hours before fitting.  If you haven't got a genuine I hope you bought a Viton (brown) seal. I always oil a seal before using.

I only use genuine seals.

Thanks for that, I'll give them a good oil bath before fitment.

---

if the gearbox & clutch is out:  yes!
 
the maincourse for leakage is mostly not the big seal but the O-Ring pos 11 19x4 behind the clutch
 

 
and if you´ve got it apart anyway:
 
change the "bitch" seal for cluch pos 12
 

Sorry for the confusion, I'm only changing the leaking rear diff seal.

When I done my final drive seal I did NOT soak in oil but I did put it in the freezer a couple of days before, it poped in easy.

With the exception of the OEM seals with a teflon lip (which have been used mostly as engine seals for around the last two decades) which mostly should be mounted dry.

It have been different submanufacturers of these during the years, from some it have also been printed on the seals that they should be mounted dry.

The days of pre soaking oil seals went out with cork seals that needed swelling before they would seal. Modern seals (in the last 40years) do not need soaking as their materials are impervious to oil and that is how they keep it in place, apart from the lip on the shaft of course.

From someone who has probably mounted more seals than I've had hot meals Follow the manufacturers instructions, if there is none which is quite common then I mount them without soaking but ALWAYS put a thin smear of lube on the seal lip and shaft surface to prevent the lip overheating from dry friction and burn the lip before the machine can supply oil to it.
Just an oily finger run around the seal will do the job you don't need to dip them in the oil can.