God, we all seem to really love the "Honker". I guess it appeals to our sense of primitive brute force engineering. That and they are cosmetically unique, big, clunky and fun to rebuild.
I understand what you meant about the audio system, but sometimes you will hear a high pitch on not only this reg but others due to a HP seat not opening up or sealing up quite fast enough, thus causing a shrill tone that can be heard as you breath. Sometimes called "piston squeak". This is independent of the audio oscillator on the Mark 7 and the noise can be carried through the LP line to the 2nd stage and is audible in the water as well. It can be confused with the audio system at times.
With regards to HP seats, what I have done on occasion if in need of a seat is to just flip the old HP seat over and use the un-marred other side and on most occasions it does just great. You just have to take a good look at the seat and ensure that it is not damaged. Of course you must do your regular service checks in all other areas but in a pinch this works.
As per lube, I not only lube this seal, as Couv says on the MKs 5,7 and 10 but also on my MK 2s of which I have 4 ( 1967-1999) and you will definitely get a better breathing 1st stage. Granted, the o-ring is held in place differently in the MK 2 but the principle is the same.
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"
Live From the Red Sea,