I had the Outback on the lift for the usual 5000 mile oil change and tire rotation and when I checked the front differential I found it low on gear oil and quite a bit of oil slung on the rh side of the front differential and cv joint shaft. I assumed the culprit was a failed cv joint shaft seal. Closer inspection revealed the area around the seal dry. Then I saw the trail of gear oil ended at the dipstick, which was quite loose in the hole. The oring on the dipstick had hardened and crystallized. I found a suitable John Deere tractor hydraulic oring and now the dipstick is nice and snug in the hole. I verified the differential vent didnt have a mud dauber nest or similar obstruction and the level is still at full and no more gear oil slinging...

yeah, our 03 had a very loose-fitting dipstick for a long time. I may need to check my replacement again.

I nursed a bad front diff bearing for a while with some Lucas additive- the thicker stuff slung up off the ring gear right up onto the bottom of the dipstick, pushed it right out!