Hi popup,
The seals in my 650 are still the originals, 6300 kms and 174 hrs right now. The 07 fork has a smaller rod internally and that creates a bit more air volume for a given depth than the earlier forks. They are also 48 mm, and yours might be smaller, so air volume is less for a given depth. Can't remember the specs, nor have I done the calcs. Frank uses generic, 'safe' numbers, and I'll rarely disagree with him because he's a bloody genius with suspension, but he also doesn't ride my bikes (very often). He has a road racing and enduro trophy collection as a rider as well as a tuner. I tend to be one of his fussier customers, but he likes that because I might not be all that fast, but I can feel and interpret what the suspension is doing and he uses that info to other's benefit. He's revalved my GTR forks a few times now, (they don't have externally adustable compression) and they are now better than the revalved and resprung Ohlins on the back. All he has done is play with the shims based on what I've asked for, still using the original valves.
The seals in my 98 501, 50 mm Extremes, running at 115 mm need changing all the time. 30hrs is about as good as it gets, and I've also rebushed them a few times too to try and improve the situation. Centre punched the bushes a bit to tighten them up as well, but no difference to seal life, and also tried Frank's recommended aftermarket and genuine seals. Being conventionals, The actual volume at 115 mm is the issue, as for all forks.
I guess the trick is to actually fill the fork, and then measure how much you remove to get the desired depth/volume when comparing different numbers. You've also played with you're travel too? If so, do they collapse further, or just extend more?
Rambling thoughts!
Steve