First off, the weight of the oil should no impact on seal failure, bottoming out repeatedly will have some effect, not necessarily because of the oil but because you have compressed the air in the fork, the fork extended has a volume of air and lets say it is atmospheric, as you compress the fork it also compress the trapped volume of air and the pressure rises. stiff adjustments will have no affect on the seals other than to say your fork won't bottom as easily and it will minimize the increased pressure in the fork tube. I set my forks up to use the whole travel without harsh bottoming, I do keep the oil changed fairly frequently, have you seen the crap that comes out, and when I do change oil I also change seals and break the fork all the way down and clean everything.
Alignment is important, if the forks are twisted in the clamps, not only does it not handle right it also does not load the fork seal evenly and can lead to premature failure.
On the K5 you unscrew the axle so not much chance of misalignment there, but on the 250 the axle goes throught the lower fork tube with a nut on the opposite side and then 4 pinch bolts this is where I've seen issues, axle gets dirty and doesn't want to go in so they use the cresent wrench to tap it in, this cause a burr on the end of the axle then as you tighten it it pulls the fork tube over causing a side load on the seal. If you have a rider that is sensitive to fork settings they can feel the bit of drag on the fork becasue of the misalignment, I can't feel the difference but have realized the importance of having everything right.
The last thing I will say is that the newer forks seem to leak easier than the older units, the fork manuf. have made bigger and bigger fork tubes and have reduced the surface area of the seal to reduce friction which could leak to premature failure.