You may not have to remove the upper head at all if you can pinpoint the exact location of the leak. There are 3 possibilities:

1. Rear cam seal. Can be changed, just a bit tricky. No need to remove upper head.

2. Leak between upper and lower head. I do not think that this likely as all oil passages under pressure are well to the center of the head. Try torquing the bolts in that area slightly say an additional 5 ft/lbs. The spec is 13 ft/lbs.

3 Oil can accumulate on top of the upper head, it seeps up the unthreaded bolt hole and out under the bolt head. This would mean that the oil under pressure has migrated across the sealed surfaces to a bolt location and up to the bolt head. This condition is common. I would try torquing them slightly in the area of the leak. You could also remove the bolts one at a time and apply a sealant under the head and re-install.

A leak between the the upper and lower heads is not a sign of impending doom. I would be inclined to try the above or live with it if the leak is not bad.

If the leak is between lower head and block that is another matter.
--
David Hunter