A few thoughts that Ive run into with my bike and MANY others...
Are you ringing OEM parts?
The fine silt (bull dust) in NV / UT / AZ and even CO has caused many fork failures (seals).
After I road off road across UT, I had a fork seal go out so bad it was just dripping on the ground. By the time I got home is was basically empty.
What volume of oil are you running? Are you pulling the spring when you measure? When you re assemble the fork are you very careful to get all the air out of everything and then double / triple check the oil volume ? Ive seen in my experience in the past of over filling and this has been 'part' of the seal issue. What oil volume do you choose to use? How many (mm) from the top are you running?
Are you on stock springs? Are you bottoming the forks out all the time? When I first got my bike I had everything pretty tight (compression / rebound / preload) I road the bike aggressive off road and bottomed out the forks ALL the time. That was my first set of seals before I went over to much stiffer custom Ohlins. Then the dust out in UT got me again. LOL
Are you running a smidge of grease on the inside of the seal before the instal ?
Are you very careful sliding the seal past the sharp edges at the top of the stanchion tube? Ive seen that damage the seal many times from others.
On the seal, (probably not likely- but double check) make sure the seal has not rolled any of the "sealing" edges. Slide it back and forth slowly just to double check.
Have you ever pulled the four guides and looked at them closely ? The Tenere is hard on guides. Ive already put three sets in my bike and I always recommend that Tenere owners change guides and seals out at the same time. Make sure there are no "particles" coming off any of the guides. If there is ANY wear, replace them. Because this is an inverted fork, the particles fall to the bottom onto the seals and because of the stroke will make the fork leak oil, even with new seals... (Ive seen this before when people have me fix there forks after they just "rebuilt", they really didnt do anything wrong other than not replace the damaged guides)
Just a few thoughts to get you past this issue !
This winter I performed the whole bike once-over. I tore down my forks to do the full service. No leaks, no major issue, just needed a full go-over.
When I pulled them down I found this on a few guides. I had already ordered the seals and guides, so I had the parts. But this is what im talking about. I see this very often in some form or fashion. Here only two pictures of one guide. I had similar pictures of my other guides............. Seals + guides