Springs that are under compression will slowly deform. I can see how the springs could get weaker over time. My hub was built in 2013 or 2014 and I have not had any such problems, but I can see how a hub that is more than a decade older than mine could have some springs that have lost some of their ability to hold the pawls tight.
And I just recalled as I typed the above paragraph, in 2019, I thought I had a bit of slippage a couple of times while on a tour. I could not remember why one generic remedy was to give a good whack to the drive side axle with the wheel out of the bike, but because I could not remember what that did, I pulled the wheel out and gave it a good whack with the rubber sole of my hiking shoe (did not kick it, used the shoe like a rubber mallet by hand). And I did not have any slippage after that. Since then, I learned that the "whack" with a rubber mallet was intended to reseat bearings and should not have anything to do with slippage. I just did a google search for Rohloff Hub rubber mallet, found a few hits, pasted this from a Rohloff manual:
The hub bearing within the
hubshell is a fixed bearing and the
hub bearing on the sprocket side is
a movable bearing. During the
replacement of the gearbox, the
movable bearing could get strained
(the outer race does not move
parallel with the inner race due to
friction created against the hub
casing). By hitting the axle pegs
with a rubber mallet, the inner and
outer races of the bearing will be
brought back into line. The
sprocket should spin freely when
rotated backwards once it is
correctly seated.
But, it appeared to have worked for me back in 2019, so you could give that a try too.
Rohloff over time has made slight changes to the hub components, I would not be surprised if they have switched to a longer or stronger spring.
I hope that springs and not pawls are the issue. I had a 1968 Triumph T100R motorcycle that I drove for about 12 years. At one time in the mid 1970s, replacement parts were extremely hard to obtain from the factory and for several months I needed a new kick starter pawl. It was only a tiny piece of steel, but because it was too worn I could not use the kick starter to start my engine. I had to push start it, which was most inconvenient.
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The area with those pawl springs appears to be the same general area that I had planned to fill up with grease when I did my next oil change in the hopes of reducing leakage. But I can easily see how adding any viscous grease would make the pawl springs a bit slower to respond when coasting.
So, maybe adding grease to that area is a bad idea?
In other words where JohnR asked: Is there enough oil / gease to keep the springs moving freely?, my concern is the opposite, would viscous grease be counter productive?
I should be doing an oil change in the next few weeks, I will keep this in mind. I plan to open it up and see if there is an obvious way to reduce leakage but I am now less inclined to add grease.