Mine is 12 years old too, with 22,300 miles. I think it was sticky in 7th to 8th as well.
Last Sept. my Rohloff wheel was squeaking. It turned out to be the rim cracking. LOL.
But before that I took the shell apart. The whole insides had a goopy black coating stuck on everything. Wipes off easy but your can't get in all the nooks.
I spent 5 hours just cleaning it. Twice I sloshed it in solvent for half an hour. Still muck coated the inside parts. Three times I dug in there around the planet gear rings with 20 Q tips. And I used folded mail paper to pull thru the little gaps. This helped but still didn't get it all.
Next day I sloshed it again in Acetone, supposed to be a bad idea. LOL That washed out really tiny specks from somewhere.
 I think I got the gaskets nicely seated with a very THIN bit of sticky grease. The gasket is actually a thin plastic, not paper. The half inch gear in the Ex box only settles in with one of the six hex sides.
It needed a new seal on the brake side and changed it. Winter came and I didn't get to ride it far yet. Way better feel now. I did the axle whack trick too. One bearing has 2 retainer rings.

There's a guy on CGOAB has a 6 page post in forums showing how he rebuilt his hub. LOL. It got full of MUD riding crazy goat tracks in SE Asia during that biblical flood they had in Nov./ Dec. Lucky they quit early and went home. He also talks about the Rohloff not so special oil he had lab tested.

There's another YT guy with a really good 45 min. video where he rebuilt the oldest hub he could find. Shell bearings too. He's a machinist so he also lathed the jigs needed.

Thank you for your kind words Dan. We were rightfully grateful to the very generous supporter and look forward to it going to its new owner who will appreciate this beautifully crafted bike.

Big thanks, Antonio

My dad had a set of those stamps...

...I do, too! As a hobbyist framebuilder, I have used them to mark my frames. It can be devilishly hard to get the numbers to register properly and fully on a rounded steel surface and the process does not take kindly to redos. I've had good luck stamping soft brass sheet stock, then silver-soldering that to the frame. I'd be happy to do so for cost of materials, but it goes beyond the usual 'blast-and-respray remit...and we're located a bit far apart!

Best, Dan.

‘I would avoid doing any work on the existing stamped number.’

Why?
It keeps the stamped number in the standard location.

From my limited experience of stamping numbers on other things it is very difficult to re-stamp an existing number as exact stamp alignment can be very hard to achieve - but careful engraving might be a way of re-establishing the serial number.


‘Another option would be if you know someone that has a set of those stamps, stamp the same number in another spot.’

Not sure that is a wise thing to do as people know where Thorn serial numbers are placed and having a number elsewhere really does make the bike look like it has been stolen!

I would avoid doing any work on the existing stamped number.  Another option would be if you know someone that has a set of those stamps, stamp the same number in another spot.  It would be best to stamp it were you can't damage anything, meaning not on a thin tube.  Perhaps a rear dropout? 

Decades ago I had a Raleigh with the number stamped on a dropout.  The number was highlighted in gold, someone in Nottingham with a very fine brush highlighted the number.

I have an Italian bike from the 1960s with the number stamped on a seatpost lug.  Example, attached.

My dad had a set of those stamps, decades ago I stamped my name on some of my tools.